A  PRACTICE  BOOK 

IN 

ELEMENTARY  METALLURGY 


BY 

ERNEST  EDGAR  THUM,  E.M. 

>\ 

Assistant  Professor  of  Metallurgy 

University  of  Cincinnati 


FIRST  EDITION 


NEW  YORK 

JOHN   WILEY   &    SONS,    INC. 
LONDON:  CHAPMAN  &  HALL,  LIMITED 

1917 


'    IV  ttbt 


Copyright,  1917 

BY 
ERNEST  EDGAR  THUM 


' 


PRESS    OF 

BRAUNWORTH    &    CO. 

BOOK    MANUFACTURERS 

BROOKLYN,     N.     Y. 


PREFACE 


SOME  two  years  ago  the  author  of  this  volume  was  confronted 
with  the  problem  of  presenting  intensive  lecture  and  laboratory 
courses  in  metallurgy  to  cooperative  students  in  mechanical, 
civil,  and  electrical  engineering  at  the  Engineering  College, 
University  of  Cincinnati.  Drawing  upon  his  own  professional 
experience,  he  concluded  that  for  such  students  the  subject 
matter  should  most  profitably  be  arranged  to  throw  light  par- 
ticularly upon  the  metallic  materials  of  engineering  construc- 
tion; how  they  are  gained  from  mother  nature;  how  they  are 
further  refined  and  worked;  and  how  their  chemical  composi- 
tion and  past  history  influence  their  various  physical  properties, 
and  their  adaptability  for  the  duty  expected  of  them. 

Some  difficulty  was  experienced  in  discovering  recent  books 
of  moderate  price  covering  the  field  of  non-ferrous  metals  and 
alloys,  as  well  as  iron  and  steel,  which  could  be  used  as  texts. 
Fortunately,  Mr.  A.  P.  Mills,  of  Cornell  University,  brought  out 
his  excellent  book  on  "  Materials  of  Construction  "  at  about 
that  time,  which  fitted  our  needs  excellently.  The  problem 
of  securing  a  laboratory  manual,  however,  presented  greater 
difficulties.  The  only  note-books  then  known  to  us  were  those 
by  H.  M.  Howe  of  Columbia  University,  and  by  Albert  Sauveur 
and  H.  M.  Boylston  of  Harvard  University.  These  books, 
altho  excellent,  did  not  seem  to  be  wholly  adaptable  to  our 
needs,  so  they  were  studied  carefully,  together  with  some  older 
laboratory  exercises  inherited  from  former  instructors,  and  a 
set  of  mimeographed  instructions  hastily  prepared  to  carry 
the  class  thru  the  first  course. 

Many  weak  points  appeared  in  every  experiment  performed. 

iii 


iv  PREFACE 

In  the  first  place,  the  limited  time  scheduled  for  the  lecture 
course  (one  semester  of  alternate  biweekly  periods — 45  lectures 
in  all)  allowed  little  or  no  time  for  the  proper  discussion  of  the 
theory  underlying  the  experiments,  and  their  applications  to 
practical  metallurgy.  In  the  second  place,  the  sketchy  instruc- 
tions left  a  good  deal  to  the  student's  own  resources — he  would 
be  running  back  and  forth  to  the  stock  room  continually  for  some 
needed  accessory  (which  might  not  be  on  hand),  or  wasting  hours 
of  valuable  time  because  he  had  neglected  some  minor  precau- 
tion. 

It  was  thought  that  engineering  students  would  be  better 
benefited  by  following  closely  a  set  of  nearly  "  fool-proof  " 
instructions  which  would  give  the  correct  results  from  which 
they  could  draw  conclusions  and  correlate  allied  information, 
rather  than  by  spending  their  time  devising  a  proper  experimental 
procedure.  With  this  in  mind,  and  with  the  added  necessity 
of  handling  classes  of  fifty  men  in  a  laboratory  equipped  with  a 
minimum  of  simple,  every-day  apparatus,  the  following  book 
was  gradually  evolved.  Nearly  the  whole  number  of  experi- 
ments have  been  performed  by  four  different  classes,  and  it  is 
hoped  that  by  now  the  text  and  instructions  are  sufficient  and 
free  from  ambiguity. 

At  the  present  time,  the  laboratory  at  the  University  of  Cin- 
cinnati has  available  the  following  general  equipment  which  is 
used  in  this  particular  course: 

Twelve  small  gas  oven  furnaces. 

One  large  hardening  furnace,  gas  fired. 

One  tilting  crucible  furnace,  gas  or  oil  fired. 

One  lead  softening  pot,  gas  fired. 

One  core  oven. 

Fifteen  millivoltmeters. 

One  Wanner  pyrometer. 

One  Morse  pyrometer. 

Ten  microscopic  photographic  sets. 

Ten  sets  of  grinding  equipment. 


PREFACE  v 

One  Brinell  hardness  machine. 

Two  scleroscopes. 

One  Olsen  impact  machine. 

Three  Howe  drop  hammers. 

One  "  Hy-temp  "  resistance  furnace. 

Two  anvils,  forges,  tool  kits,  etc. 

It  is  therefore  apparent  that  approximately  fifty  students, 
divided  into  twelve  squads  of  about  four  each,  will  have  a  gas 
furnace  and  pyrometer  for  each  squad.  A  certain  rotation  of 
the  work  is  of  course  necessary  after  the  first  few  days,  in  order 
that  each  squad  may  have  a  separate  day  at  the  refractory 
experiment,  No.  4,  which  uses  the  electrical  resistance  furnace; 
the  hardness  experiment,  No.  13,  which  uses  the  Brinell  machine 
and  the  scleroscopes;  the  metallography  experiment,  No.  n, 
which  involves  individual  microscopes;  and  so  on. 

While  the  instructions  on  first  glance  seem  to  be  for  one 
particular  laboratory  and  set  of  equipment,  a  closer  inspection 
will  discover  a  sincere  effort  to  make  the  text  applicable  to 
considerable  variations  in  material.  Entire  generality  would 
have  defeated  its  own  purpose,  as  explained  at  some  length, 
above.  Thus,  while  experiment  No.  i  must  illustrate  one 
particular  furnace,  and  that  furnace  naturally  is  the  one  in 
use  at  this  laboratory,  still  the  methods  of  operation  are  uni- 
versally applicable  to  all  gas  furnaces.  The  thermo-couple 
experiments  Nos.  6,  7,  and  9  require  merely  a  millivoltmeter 
or  a  potentiometer.  And  so  on — in  fact,  a  very  large  percentage 
of  the  pieces  of  apparatus  called  for  has  been  taken  from  stock 
in  the  chemical  storeroom,  or  purchased  at  local  hardware  stores. 

While  it  is  hoped  that  this  book  and  its  methods  may  appeal 
to  officers  now  in  charge  of  better  equipped  laboratories,  and  help 
emancipate  them  from  the  nuisance  of  mimeographed  instruc- 
tion sheets,  it  is  thought  certain  that  it  will  appeal  more  force- 
fully to  instructors  who,  like  the  author,  are  confronted  with  the 
problem  of  building  up  a  respectable  laboratory  course  with  a 
modest  amount  of  equipment,  funds,  time,  and  assistance. 


vi  PREFACE 

It  is  a  pleasure  gratefully  to  acknowledge  my  indebtedness 
to  Mr.  E.  P.  Stenger,  Met.E.,  Instructor  in  Metallurgy,  Uni- 
versity of  Cincinnati,  for  his  continual  care  in  the  immediate 
supervision  of  the  laboratory  work,  which  has  brought  forth 
numberless  perfections  in  the  details  of  the  experiments;  and 
to  Mr.  Clyde  William  Park,  A.M.,  Associate  Professor  of  English, 
and  Mr.  W.  Otto  Birk,  M.A.,  Instructor  in  English,  University 
of  Cincinnati,  who  have  each  critically  examined  portions  of  the 
manuscript. 

E.  E.  THUM. 

CINCINNATI,  OHIO, 
June  i,  1917- 


TABLE   OF   CONTENTS 


PAGE 

GENERAL  RULES  AND  INSTRUCTIONS i 

EXPERIMENTAL  GROUP  I 

1 .  Furnace  Operations 7 

2.  Oxidizing  Reactions 12 

3.  Reducing  Atmospheres  and  Reactions 18 

4.  Refractories 25 

5-  Slags 32 

EXPERIMENTAL  GROUP  II 

6.  Thermo-couple  Elements 41 

7.  Thermo-couple  Construction 49 

8.  The  Cooling  Curve  of  a  Pure  Substance 56 

9.  Thermo-couple  Calibration 63 

10.  Lead-antimony  Alloys 70 

EXPERIMENTAL  GROUP  III 

11.  Metallography 79 

1 2.  Photomicrography 86 

13.  Hardness 94 

14.  Electric  Furnaces 102 

15.  Radiation  and  Optical  Pyrometers in 

EXPERIMENTAL  GROUP  IV 

16.  Transformation  Points 125 

1 7.  Crystallization  of  Steel 133 

18.  Hardening  of  Steel 141 

19.  Quenching  Media 147 

20.  Tempering  and  Toughening 152 

21.  Tool  Making 162 

22.  Metallography  of  Steel 167 

23.  Case  Carburizing 180 

24.  Corrosion 194 

vii 


viii  CONTENTS 

EXPERIMENTAL  GROUP  V  PAGE 

25.  Molding 209 

26.  Composition  of  Cast  Iron 213 

APPENDICES 

A.  Elementary  Metallurgical  Calculations 225 

B.  Foundry  Practice 269 

C.  Instructions  for  Written  Work 292 

INDEX 302 


METALLURGICAL   LABORATORY 


GENERAL   RULES   AND   INSTRUCTIONS 

Enrollment.  Students  cannot  be  enrolled  for  the  laboratory 
work  until  they  have  exhibited  receipts  from  the  registrar  show- 
ing that  they  have  paid  the  fees,  and  made  the  necessary  cash 
deposits.  A  coupon  ticket  will  be  given  the  student  in  exchange 
for  his  breakage  deposit  receipt.  Extra  supplies  and  new 
apparatus  to  replace  breakage  may  be  purchased  with  these  cou- 
pons. Whenever  this  ticket  is  reduced  to  a  value  of  $2.00, 
the  stock  clerk  may  require  an  additional  deposit  of  $5.00  before 
issuing  further  supplies.  A  certificate  of  refund  will  be  issued 
on  the  completion  of  the  course,  covering  the  amount  of  the 
deposit,  less  any  deductions  punched  out  of  the  coupon  ticket. 

Attendance.  The  laboratory  is  regularly  open  from  1:00 
P.M.  until  5:00  P.M.  The  roll  will  be  taken  at  one  o'clock  by 
visiting  the  various  furnaces  and  ascertaining  the  names  of  the 
men  present  for  work.  While  in  the  laboratories,  the  students 
will  be  expected  to  conduct  themselves  in  an  industrious  and 
orderly  manner. 

Squad  Organization.  The  members  of  the  class  will  be 
divided  into  squads  at  the  beginning  of  the  semester.  Each 
squad  is  intended  to  work  as  a  unit  at  the  assigned  furnace,  under 
the  general  direction  of  the  captain.  A  student  will  act  as  cap- 
tain of  his  squad  for  a  period  of  two  weeks;  his  name  will  be 
posted  on  the  bulletin  board  at  the  beginning  of  the  period, 
and  he  will  be  responsible  for  the  orderly  prosecution  of  the  work, 
the  care  of  the  equipment,  and  the  condition  of  the  laboratory 
work  tables  during  that  time. 


2  GENERAL  RUIES  AND  INSTRUCTIONS 

General  Apparatus.  There  is  a  certain  amount  of  equipment 
more  or  less  common  to  all  experiments;  this  apparatus  will  be 
furnished  each  squad  and  it  is  to  be  cared  for  by  them.  The 
movable  parts  are  to  be  kept  in  the  lockers  assigned  for  that 
purpose  and  locked  with  the  padlocks  furnished  by  the  stock 
keeper.  The  metal  parts  of  furnaces  kept  on  top  of  the  desks 
are  to  be  blackened  at  the  end  of  each  week.  At  the  end  of  the 
semester  the  contents  of  the  lockers  will  be  inspected  by  the 
storekeeper,  and  any  abuse  of  equipment  or  loss  of  material 
will  be  charged  equally  among  the  members  of  the  squad  on  their 
breakage  tickets.  This  equipment  for  each  squad  is  as  follows: 

Oven  furnace,  Pot  furnace  and  lid, 

Blast  lamp,  Three  pieces  rubber  gas- tubing, 

Bunsen  burner,  Button  mold, 

4o-mesh  screen,  pan  and  cover,  Horseshoe  magnet, 

Tripod,  Wire  gauze, 

Box  of  matches,  Taper  holder, 

Ring  stand  and  clamp,  Quart  pail, 

Pint  glass  tumbler,  Scorifier  tongs, 

Crucible  tongs,  Machinist's  hammer, 

Blacksmith's  tongs  for  f  in.  Screw-driver, 

rounds,  Two  hack-saw  blades, 

Wire-cutting  pliers,  Spatula, 

Hack-saw  frame,  Mixing  cloth, 

Triangular  file,  Piece  of  emery  cloth, 

Marking  pencil,  Asbestos  mittens, 

Counter  brush,  Can  of  stove  polish, 

Used  clay  crucible,  10  gm.,  Polishing  brush. 

Personal  Apparatus.  Each  student  in  the  metallurgical 
laboratory  should  own  a  pair  of  safety  goggles,  which  must  be 
worn  when  lighting  furnaces,  welding  at  the  arc,  using  the  emery 
wheel,  or  pouring  hot  metal.  Disregard  of  these  elementary 
safety  precautions  will  be  sufficient  cause  for  expulsion  from  the 
laboratory.  Any  accident  must  be  reported  immediately  to  an 
instructor,  who  will  give  necessary  aid,  or  summon  a  physician. 


GENERAL  RULES  AND  INSTRUCTIONS  3 

Students  should  also  carry  a  rule  or  tape  of  some  design. 
The  use  of  a  slide-rule  is  recommended. 

Special  Apparatus.  The  captain  of  each  squad  will  each  day 
receive  a  tray  from  the  stock  room  containing  the  special  appa- 
ratus needed  for  each  experiment.  He  will  sign  a  receipt  for 
this  material,  and  be  responsible  for  its  safe  return  in  good  order 
at  the  end  of  the  period.  Any  loss  or  breakage  will  be  assessed 
among  the  members  of  the  squad. 

Supplies.  A  sufficient  quantity  of  supplies  for  the  per- 
formance of  each  experiment  will  be  issued  to  the  captain  of 
each  squad  at  the  beginning  of  the  afternoon.  In  case  of  care- 
less wastage,  a  new  supply  must  be  purchased  with  the  coupon 
book.  Supplies  are  not  returnable,  but  should  be  reserved  in  a 
locker,  as  many  times  the  materials  are  to  be  used  in  a  subse- 
quent experiment.  Hot  crucibles  may  be  left  overnight  under 
the  furnace  in  an  orderly  array,  but  will  be  removed  by  the 
janitors  at  the  week  end. 

Laboratory  Equipment.  A  certain  amount  of  large  or 
expensive  apparatus  for  common  use  at  intervals  by  all  squads 
is  listed  in  each  experiment.  This  equipment  will  be  located 
at  suitable  points  in  the  laboratory.  A  decent  consideration 
of  the  rights  of  the  other  students  will  insure  its  proper  use  and 
care. 

Texts.  The  laboratory  instruction  book  is  to  be  used  as  an 
auxiliary  to  the  class-room  text,  and  the  lesson  assignments 
which  will  be  posted  at  the  beginning  of  the  year,  or  from  time 
to  time,  should  be  studied  at  the  date  specified.  The  actual 
laboratory  work  for  each  day  will  have  been  posted  at  some 
preceding  period.  Each  student  is  expected  to  have  read  over 
the  instructions  for  the  day's  work  before  entering  the  laboratory 
in  order  that  the  work  may  proceed  promptly  and  intelligently. 
The  instructions  have  been  worked  out  in  detail  so  that  correct 
results  may  be  expected  if  the  precautions  are  carefully  observed. 
The  references  given  may  be  consulted  when  convenient,  to 
obtain  a  more  elaborate  discussion. 

Inspection.    When  the  experiment  assigned  has  been  com- 


4  GENERAL  RULES  AND  INSTRUCTIONS 

pie  ted,  an  instructor  should  be  called  to  your  furnace  and  the 
results  of  the  experiment  together  with  all  preliminary  computa- 
tions and  sheets  of  neat  tabulations  of  acquired  data  should 
be  exhibited  for  his  inspection  and  "O.K."  On  receiving 
this  approval,  students  are  at  liberty  to  leave  the  laboratory  if 
the  squad  is  up  to  schedule.  The  captain  will  be  expected  to 
see  that  the  laboratory  tools  are  left  in  an  orderly  arrangement 
and  in  their  correct  location.  All  dirt  is  to  be  brushed  off  the 
table  tops;  movable  apparatus  locked  up;  special  apparatus 
returned  to  the  stock  room;  and  the  furnace  cleaned  on  the 
inside,  on  top,  and  underneath. 

Written  Work.  The  results  of  each  line  of  procedure  should 
be  recorded  in  a  clear,  concise,  and  definite  statement.  Discus- 
sion of  these  results  should  follow  in  the  order  of  procedure  listed 
in  the  printed  instructions.  The  statement  of  results  and  the 
solution  of  the  assigned  queries  are  the  only  written  exercises 
required  of  the  student.  It  is  not  necessary  to  recount  the 
method  of  performing  the  experiment,  since  this  would  be  merely 
a  paraphrase  of  the  printed  instructions.  All  written  work 
should  be  well  and  neatly  done  on  standard  paper,  following  the 
general  directions  for  written  work  in  Appendix  C. 

Queries.  Following  the  procedure  in  each  experiment  is 
a  list  of  queries,  some  of  which  are  for  more  advanced  students. 
Each  student  should  therefore  consult  the  bulletin  board  for 
information  as  to  the  particular  queries  required  from  his  class. 
These  are  to  be  worked  out  and  written  up  by  each  man  indi- 
vidually. Problems  and  computations  must  be  solved  in  an 
orderly  manner,  with  all  steps  shown  and  noted,  so  that  they  can 
be  readily  checked  over. 

The  instructor  can  observe  the  results  of  the  experiment, 
and  will  grade  the  student's  skill  in  manipulation  during  the 
laboratory  period.  The  queries,  on  the  other  hand,  are  designed 
to  show  him  whether  the  individual  student  comprehends  the 
theory  underlying  the  experiment  and  can  interpret  the  results. 
A  high  grade  will  be  given  work  evidencing  thought  and  indi- 
viduality, even  tho  the  correct  solution  is  not  attained.  For 


GENERAL  RULES   AND   INSTRUCTIONS  5 

this  reason,  it  is  also  clear  that  squad  work  on  the  written  part 
cannot  be  accepted.  Stand  on  your  own  feet!  When  you  are 
past  school  age  it  will  not  always  be  so  easy  to  turn  to  a 
"  wizard  "  at  your  elbow  for  an  explanation  of  the  knotty 
points. 

Curves.  Acceptable  curves  must  be  neatly  drawn  to  scale 
and  lettered  with  India  ink  on  standard  cross-section  paper. 
Title  the  curves  and  the  coordinates,  following  the  directions  in 
the  appendix.  Sign  and  date  each  curve  sheet.  We  want 
curves  made  by  engineers. 

Submission  of  Written  Work.  All  written  work,  queries, 
curves,  and  tabulations  of  data,  are  to  be  bound  together  in  a 
regular  Metallurgical  Laboratory  binder  of  cardboard  and 
submitted  to  the  instructor  in  charge  at  the  end  of  each  bi- 
weekly school  period.  This  binder  would  therefore  contain 
reports  on  all  the  work  since  the  last  submission  of  data.  After 
examination  and  grading,  this  work  will  be  returned  to  the  student 
for  his  own  reference,  and  is  to  be  retained  subject  to  call  by  the 
English  Department.  It  is  important  that  the  covers  and  con- 
tents be  preserved  intact,  as  they  must  be  resubmitted  in  case 
of  conditions  or  unsatisfactory  work. 

Grades.  Final  grades  for  laboratory  courses  will  be  based 
upon  daily  marks  on 

ist,  the  queries; 

2d,  the  results  of  the  laboratory  work,  inspected  day  by  day; 

3d,  written  work  other  than  queries; 

4th,   general  conduct  and  industry  during  the  laboratory 

period ; 
5th,  attendance. 

It  is  essential  for  the  orderly  conduct  of  affairs  in  the  labor- 
atory that  all  notes  be  kept  up  to  date  and  be  submitted  promptly 
according  to  schedule.  In  case  a  student  fails  in  punctuality, 
his  work  will  receive  but  75  per  cent  the  mark  it  otherwise  would 
obtain. 


EXPERIMENTAL  GROUP  I 
FOREWORD  TO   THE   STUDENT 

In  Experiments  Nos.  i  to  5  inclusive  are  presented  a  number 
of  general  experiments  which  form  an  introduction  to  the  study 
of  metallurgy. 

Laboratory  work  in  metallurgy  is  largely  confined  to  the  study 
of  the  behavior  of  solids  at  moderately  high  heat.  It  is  essential, 
therefore,  that  the  first  experiment  should  instruct  the  student 
in  the  furnace  provided  for  obtaining  these  temperatures. 

Systematic  metallurgy  naturally  starts  with  the  production 
of  the  pure  metals  from  the  compounds  or  salts  found  in  nature. 
The  chemical  processes  involved  in  these  operations  are  quite 
dissimilar  to  the  test-tube  reactions  with  which  the  student 
is  already  familiar.  Experiments  Nos.  2  and  3,  on  oxidizing 
and  reducing  reactions,  are  given  in  order  that  the  student  may 
adjust  his  state  of  mind  to  the  metallurgical  viewpoint. 

In  the  reduction  of  metallic  oxides,  high  temperature  reac- 
tions proceed  continuously  in  certain  containers.  These  fur- 
naces or  crucibles  must  be  able  to  withstand  the  high  heat  with- 
out melting  or  corroding.  Experiment  No.  4  on  refractories 
is  designed  to  show  the  relative  infusibility  of  some  common 
brick-making  materials. 

These  selfsame  refractory  materials,  however,  are  normally 
present  in  most  metallic  ores;  and  Experiment  No.  5  on  slags 
is  designed  to  demonstrate  how  these  relatively  infusible  mate- 
rials can  be  removed  from  a  furnace  in  a  molten  condition. 

Each  experiment  endeavors  to  present  in  a  logical  manner 
a  clear  statement  of  the  underlying  principles  of  the  process 
under  consideration,  together  with  notes  as  to  its  commercial 
applications.  Carefully  follow  the  details  of  the  procedure, 
and  the  proper  results  are  assured.  Then  attempt  to  visualize 
the  grand  scale  of  metallurgical  operations  in  the  light  of  your 
laboratory  practice. 


EXPERIMENT  NO.   1 


FURNACE  OPERATIONS 

Object.     This  experiment  is  an  introduction  to  the  opera- 
tion of  gas  furnaces. 

General  Explanation.  The  oven  furnace  in  use  in  this  lab- 
oratory (Fig.  i)  consists  of  an  iron  box  lined  with  fire  brick, 
with  three  gas  burners  operating  thru  each  side  wall,  near 
the  bottom.  A  short  distance  above  the  bottom  is  placed  a 
fire-clay  shelf  which  constitutes 
the  working  floor  of  the  furnace 
and  forms  the  roof  of  a  com- 
bustion chamber  in  which  the 
incoming  gas  and  air  combine. 
The  hot  products  of  combus- 
tion pass  thru  the  opening  be- 
tween the  edge  of  the  shelf  and 
the  side  walls  into  the  furnace 
"  laboratory  "  above,  and  thence 
escape  thru  two  vents  in  the 
ceiling.  Natural  gas  is  the  fuel 
used;  sufficient  air  under  press- 
ure is  also  supplied  to  become 
intimately  mixed  with  the  gas 
and  support  perfect  combustion.  The  maximum  temperature 
may  be  attained  by  close  regulation  of  the  gas  and  air — an 
excess  of  gas  will  as  effectively  cool  the  flame  as  an  excess 
of  air.  Therefore,  a  neutral  atmosphere  will  generally  give  a 
higher  calorific  intensity  than  either  an  oxidizing  or  a  reducing 
flame. 

Methods  of  measuring  the  temperatures  in  a  furnace  are  of 

7 


FIG.  i. — Oven  Furnace. 


8 


EXPERIMENTAL  GROUP  I 


course  very  important.  One  of  the  earliest  systems  in  use  is 
that  of  observing  the  melting-point  of  Seger  cones,  so  called 
after  their  originator.  These  cones  are  made  of  various  mix- 
tures of  alumina,  silica,  alkaline  oxides,  etc.,  whose  melting 
or  softening  temperatures  are  fairly  well  determined.  Each 
cone  has  a  number  stamped  on  the  side  corresponding  to  a  defi- 
nite composition.  When  the  cone  is  gradually  heated  up  and 
approaches  its  melting-point,  the  mixture  softens  and  the  peak 
of  the  cone  starts  to  bend  over.  When  the  apex  is  bent  over  in 
an  approximately  horizontal  direction  it  has  attained  the  tem- 
perature corresponding  to  the  number  which  it  bears,  as  given 
in  the  following  list: 


No. 

Temp. 

No. 

Temp. 

No. 

Temp. 

No. 

Temp. 

022 

600 

070 

960 

9 

1280 

-29 

1650 

021 

650 

o6a 

980 

IO 

1300 

30 

1670 

O2O 

670 

050 

IOOO 

II 

1320 

31 

1690 

OIQ 

690 

040 

IO2O 

12 

I3SO 

32 

1710 

018 

710 

030 

IO4O 

13 

1380 

33 

1730 

017 

730 

02(1 

IO6O 

14 

1410 

34 

I7SO 

016 

750 

Old 

I080 

15 

1435 

35 

1770 

oi  50 

790 

Id 

IIOO 

16 

1460 

36 

1790 

014*1 

815 

2d 

1  1  20 

17 

1480 

37 

1825 

0130 

835 

3« 

1140 

18 

1500 

38 

1850 

0120 

855 

4a 

1160 

19 

1520 

39 

1880 

oirfl 

880 

5« 

1180 

20 

I53P 

40 

1920 

oioa 

900 

6a 

1200 

26 

1580 

4i 

1960 

090 

920 

7 

1230 

27 

1610 

42 

2OOO 

o8a 

940 

8 

1250 

28 

1630 

Note  that  all  temperatures  in  this  list  are  degrees  Centigrade. 

Special  Apparatus.     The   special   apparatus  needed  is  as 
follows: 

Seven  scorifiers. 
Supplies.    The  supplies  needed  are  as  follows: 

Seger  cones  Nos.  021,  017,  013(1,  o8a,  040,  ia,  40. 

Sand. 

Charcoal. 


FURNACE  OPERATIONS  9 

Procedure,  a.  Exhibit  your  receipts  to  a  laboratory  officer 
showing  proper  payment  of  laboratory  fees  and  deposit.  This 
is  an  absolute  requirement  which  the  student  must  fulfil  before 
he  will  be  allowed  to  do  any  work  in  the  laboratory. 

b.  Properly  registered  students  will  be  grouped  into  squads 
for  laboratory  work.     The  personnel  of  these  squads  will  remain 
fixed  for  the  semester  and  can  be  changed  only  by  permission. 

c.  A  laboratory  officer  will  read  the  "  General  Rules  and 
Instructions  "    (pages  i  to   5),  and  identify  the  general  appa- 
ratus comprising  the  equipment  of  each  squad.     He  will  also 
demonstrate  the  method  of  lighting  the  furnace. 

d.  After   the  blower  has  been   started,   open   the  door   of 
the  furnace  and  place  a  flame  on  the  inside  of  the  furnace  by 
means  of  the  taper  holder.     Open  the  gas  cock  wide;   and  when 
the  flame  flares  up,  remove  the  taper  holder  from  the  furnace. 
The  valve  with  the  hand  wheel  regulates  the  gas  supply,  while 
the  valve  which  is  operated  by  means  of  a  lever  regulates  the 
air.     The  flame  of  the  burning  gas  will  now  be  projecting  from 
the  door  and  the  vents  of  the  furnace. 

e.  Turn  on  the  full  air  supply  and  then  throttle  down  the 
gas   very  slowly,    constantly   shortening   the    flame   until    the 
mixture  of  gas  and  air  is  such  that  the  combustion  takes  place 
entirely  within  the  furnace  and  under  the  hearth.     Be  sure 
that  the  furnace  door  is  open  and  that  no  one  is  standing  in 
front  during  these  manipulations,  because  when  the  mixture 
of  gas  and  air  is  just  right,  an  explosion  wave  carries  the  flame 
from  the  furnace  openings  back  to  the  gas  burners  in  the  combus- 
tion chamber.     Note  the  tune  when  the  flame  begins  to  burn 
satisfactorily,  and  close  the  door. 

/.  Fix  each  of  the  Seger  cones  upright  in  a  scorifier  of  sand. 
Arrange  these  scorifiers  in  the  furnace  in  a  definite  order  so  that 
the  location  of  each  cone  is  known.  Note  the  condition  of 
the  cones  from  time  to  tune  while  the  furnace  is  heating  up. 
Record  the  time  when  the  apex  of  each  cone  is  bent  over  hori- 
zontally; the  furnace  has  then  reached  the  temperature  corre- 
sponding to  that  number.  Note  also  the  color  of  the  light 


10  EXPERIMENTAL  GROUP  I 

radiated  by  the  interior  of  the  furnace.  An  experienced  man 
can  give  a  remarkably  close  estimate  of  the  temperature  of  his 
furnace  or  of  a  piece  of  hot  metal  by  its  color. 

g.  After  the  furnace  has  apparently  reached  its  maximum 
temperature,  request  an  instructor  to  inspect  its  condition, 
remove  the  scorifiers,  and  place  a  piece  of  charcoal  in  the  fur- 
nace. Then  throttle  down  the  amount  of  gas  carefully  until 
the  charcoal  glows  brightly.  This  glow  shows  that  oxidizing 
conditions  prevail  in  the  furnace,  since  the  charcoal  is  now 
burning  in  the  excess  of  air  present.  By  turning  on  an  excess 
of  gas,  the  reducing  atmosphere  is  produced,  which  is  evidenced 
by  a  thin  gas  flame  burning  on  the  exterior  of  the  furnace. 
Note  the  condition  of  the  charcoal  under  these  conditions. 
The  neutral  condition  occurs  when  perfect  combustion  is  taking 
place;  that  is,  when  neither  an  excess  of  gas  nor  air  is  present. 
This  condition  is  obtained  when  neither  the  gas  burns  at 
the  exterior  of  the  furnace,  nor  the  charcoal  glows  on  the 
hearth. 

h.  Re-read  this  entire  experiment  carefully,  and  be  sure 
that  you  understand  the  text,  have  performed  all  the  manipula- 
tions, and  can  answer  the  required  queries. 

i.  When  the  experiment  is  finished,  exhibit  the  data  to  a 
laboratory  officer.  If  it  is  satisfactory,  return  the  special 
apparatus  to  the  stock-room,  and  clean  up  your  premises. 

Queries,  a.  Briefly  describe  the  construction  of  the  furnace, 
together  with  the  gas  and  air  piping,  and  illustrate  the  descrip- 
tion with  a  neat  pen-and-ink  sketch. 

b.  Draw  a  curve  showing  the  rate  at  which  the  furnace 
was   heated,    according    to    the   instructions   on  page    5,    and 
Appendix  C.     Note  the  colors  corresponding  to  various  tem- 
peratures on  this  curve. 

c.  What  causes  the  difference  in  the  appearance  of  the  gas 
flame  under  oxidizing  and  reducing  conditions? 

d.  Explain  fully  the  reasons  for  the  statement  that  a  neutral 
flame  will  give  the  highest  temperatures. 

e.  Cite  various  heating  operations  where  it  is  important 


FURNACE  OPERATIONS  11 

to  maintain  a  reducing,  an  oxidizing,  or  a  neutral  atmos- 
phere. 

/.  Why  are  Seger  cones  placed  in  a  scorifier  and  not  on 
the  bottom  of  the  furnace? 

g.  Discuss  the  limitations  in  using  Seger  cones  for  pyrom- 
eters. 


EXPERIMENT  NO.  2 
OXIDIZING  REACTIONS 

Object.  The  object  of  this  experiment  is  to  reproduce  in 
the  laboratory  some  of  the  oxidizing  reactions  used  in  metallurgy. 

General  Explanation.  By  the  term  "  oxidizing  reaction  " 
the  metallurgist  means  a  chemical  interchange  which  will 
convert  some  metal  or  metallic  compound  into  a  corresponding 
metallic  oxide. 

Oxygen  is  the  most  abundant  element  known,  comprising 
perhaps  50  per  cent  of  the  entire  earth  mass.  In  the  free  state 
it  forms  23  per  cent  of  the  atmosphere,  by  weight.  Combined, 
it  forms  eight-ninths  of  the  water,  half  the  sand,  and  a  large 
proportion  of  most  of  the  existing  mineral  and  organic  substances. 
Oxygen  has  taken  part  in  important  reactions  during  the  for- 
mation of  the  earth  materials,  quartz  or  sand  being  the  result 
of  the  oxidation  of  the  metalloid  silicon: 


=  Si02  +  196,000. 

Silica  is  an  important  substance,  inasmuch  as  large  quantities 
are  found  pure,  and  doubly  so  as  it  is  an  essential  component 
of  all  volcanic  rocks.  Water  is  likewise  the  product  of  the 
oxidation  of  the  metal  hydrogen: 

2H2+O2  =  2H2O+i38,ooo  (liquid). 

Owing  to  the  presence  of  an  excess  of  free  or  combined  oxygen 
in  all  processes,  unless  carefully  excluded,  and  to  the  strong 
affinity  of  most  metals  for  oxygen,  the  wasting  away  of  pure 
metals  by  the  formation  of  their  oxides  is  a  comparatively  rapid 
process.  This  oxidation,  when  it  goes  forward  slowly  as  the 
result  of  exposure  to  atmospheric  agencies  is  known  as  "  corro- 

12 


OXIDIZING  REACTIONS  13 

• 

sion."  Oxidation  of  heated  metal  in  rolling  or  forging  is  much 
more  rapid,  and  causes  large  losses  as  "  mill  scale  ";  the  reac- 
tion is  as  follows: 


Because  of  these  facts,  the  common  metals  are  found  in  nature 
in  an  oxidized  condition,  the  principal  ores  of  iron,  for  instance, 
being  hematite,  limonite  and  magnetite. 

The  oxidation  of  pure  metals  is  a  common  operation  in  mak- 
ing pigments,  or  in  recovering  rare  metals.  In  the  first  case, 


is  extensively  practiced  to  make  the  body  for  the  best  white 
paints.  In  the  second  instance,  the  metallic  lead  produced  in 
lead  smelting  carries  with  it  the  gold  and  silver  contained  in 
the  furnace  charges,  which  metals  are  often  separated  by  a  proc- 
ess called  "  cupellation,"  wherein  the  molten  lead  is  exposed 
to  a  current  of  air  which  oxidizes  it  to  litharge.  This  lead  oxide 
is  then  drawn  off  or  "  skimmed  "  from  the  remaining  metal  while 
the  rarer  metals  will  resist  oxidation  to  the  last.  The  reac- 
tion is  as  follows: 

2Pb+O2  =  2PbO+  101,600. 

Sulfur  is  an  element  somewhat  similar  in  chemical  proper- 
ties to  oxygen  —  in  fact,  ore  bodies  of  metallic  oxides  found  near 
the  surface  often  change  by  degrees  into  bodies  of  the  corre- 
sponding sulfides,  the  oxidized  portions  having  been  formed  from 
the  original  sulfide  enrichment  by  the  action  of  percolating 
surface  water  containing  oxygen  and  carbon  dioxide  in  solu- 
tion. In  fact,  most  metallic  ores  are  deposited  in  the  first 
instance  as  sulfides  from  hot  alkaline  solutions  rising  from 
the  depths  thru  fissures  in  the  earth's  crust.  The  oxidized 
ores  are  distinctly  secondary  —  that  is,  have  been  formed  from  the 
primary  sulfide  deposits  at  a  later  time.  The  elimination  of 
sulfur  from  these  sulfide  ores  is  the  prime  reason  for  "  roasting  " 
operations  (see  pages  262,  548,  568,  Mills,  "  Materials  of  Con- 


14  EXPERIMENTAL  GROUP  I 

• 

struction  "),  and  they  may  be  classed  under  oxidizing  reac- 
tions because  the  metallic  sulfides  are  changed  into  oxides,  often 
with  an  increase  in  valence,  while  the  sulfur  which  is  eliminated 
burns  to  sulfur  dioxide  (SCb).  Non-ferrous  smelting  plants 
liberate  such  enormous  quantities  of  this  gas  as  to  become  verit- 
able nuisances  in  spite  of  the  most  modern  appliances  for  puri- 
fying the  smoke. 

Special   Apparatus.    The   special   apparatus   needed   is    as 
follows : 

One  piece  of  f-in.  iron  pipe,  about  6  in.  long. 

One  roasting  dish. 

Two  test  tubes. 

One  test-tube  holder. 

One  funnel. 

One  blowpipe,  and  burner-tip. 

Supplies.     The  supplies  needed  are  as  follows: 

Zinc  button,  about  20  gm. 

Lead  button,  about  125  gm. 

Heavy  iron  wire,  about  8-gage,  3  ft.  long. 

Thin  iron  wire,  about  4o-gage,  12  in.  long. 

Two  scorifiers. 

One  piece  of  soft  glass  tubing,  6  in.  long. 

Laboratory  Equipment.     The  laboratory  equipment  needed 
is  as  follows: 

Anvil. 

Two  bucking-boards  and  mullers. 

Piece  of  |-in.  pine  board. 

Package  of  filter  papers. 

Coke. 

Pyrite. 

Charcoal. 

Sodium  carbonate  crystals. 

Ammonia. 

Distilled  water. 


OXIDIZING  REACTIONS  15 

Procedure.     NOTE  :  Start  parts  b  and  c  simultaneously. 

a.  Make  a  "  rabble  "  for  stirring  pyrite  in  this  manner: 
Heat  one  end  of  the  8-gage  iron  wire,  flatten  it  out  thin  on  an 
anvil,  and  bend  the  thin  end  over  square,  forming  a  small  hoe, 
the  blade  of  which  will  be  about  f  in.  wide  by  \  in.  high. 

6.  Polish  the  fine  wire  until  it  is  bright,  twist  it  into  a  spiral 
around  a  pencil,  then  insert  it  into  the  iron  tube  and  place 
the  whole  in  a  cold  furnace.  At  the  end  of  the  afternoon 
examine  the  condition  of  the  wire,  and  reserve  it  for  comparison 
with  the  results  of  Experiment  No.  3. 

c.  Break  up  to  rice  size  sufficient  pyrite  (FeS2)  to  cover  the 
bottom  of  the  roasting  dish  f  in.  deep;  place  the  dish  in  a  cold 
oven  furnace  near  the  open  door.     Bring  the  heat  up  to  a  low 
red  with  an  oxidizing  flame,  keeping  the  front  door  open  all  the 
time.     Note  the  condition  of  the  ore  and  stir  carefully  but 
thoroly  with  the  rabble  at  ten-minute  intervals.      CAUTION: 
Do  not  overheat  the  roast. 

d.  Near  the  end  of  the  laboratory  period  remove  the  dish, 
cool,  and  pulverize    the   contents   until  it  will  all  pass  thru 
a  4o-mesh  screen.     Place  this  ground  material  on  a  piece  of  paper, 
and  separate  magnetite  (FeaCU)  and  pyrrhotite  (FeeS?)  with 
a  magnet.     Test  for  soluble  iron  sulfate  (FeSCU)  by  placing  the 
non-magnetic  part  in  a  test  tube  and  boiling  with  distilled 
water.     Filter  and  add  a  few  drops  of  ammonia  to  the  filtrate. 
Ferrous  hydrate  is  white;    a  darker  colored  precipitate  shows 
the  presence  of  soluble  ferric  compounds.     Test  the  magnetic 
part  and  also  the  residue  held  on  the  filter  paper  by  igniting 
a  little  of  each  with  sodium  carbonate  on  charcoal  in  a  reducing 
blowpipe  flame.     Crush  the  resulting  bead,  place  it  on  a  clean 
silver    coin    and    moisten.     Black   silver   sulfide   forming  will 
evidence  the  presence  of  undecomposed  sulfides  in  the  roasted 
material. 

e.  Powder  500  gm.  of  coke.     Place  20  gm.  of  zinc  in  a  scori- 
fier  and  heat  in  a  pot  furnace  in  a  strongly  oxidizing  flame  until 
it  catches  fire,  then  smother  the  flame  with  powdered  coke. 

/.  Draw  the  glass  tube  down  to  form  an  air  nozzle  about 


16  EXPERIMENTAL   GROUP  I 

i  mm.  in  diameter.  Place  a  scorifier  containing  about  125  gm. 
of  lead  upon  a  used  crucible,  set  inverted  in  the  pot  furnace. 
Cover  the  furnace  and  heat  the  lead  to  a  dull  red  color.  Skim 
off  any  dross  with  a  sliver  of  wood,  and  adjust  the  flame  of  the 
blast  lamp  by  carefully  controlling  the  gas  supply  until  the 
surface  of  the  lead  button  remains  clear.  Then  carefully  pro- 
ject a  blast  of  air  thru  the  glass  nozzle  upon  the  molten  lead 
with  sufficient  force  just  to  dimple  the  surface,  but  not  forceful 
enough  to  splatter  the  hot  metal.  The  formation  of  litharge 
(PbO)  by  reaction  between  the  molten  lead  and  the  oxygen  of 
the  air  must  proceed  rapidly  in  order  to  counteract  losses  by 
volatilization  of  the  oxide,  and  the  formation  of  lead  silicates 
by  reaction  with  the  material  of  the  scorifier.  When  the  sur- 
face of  the  lead  is  nearly  covered  with  the  molten  oxide,  pour 
the  whole  rapidly  into  a  button  mold.  When  cool,  break  off 
the  brittle  oxide  on  a  bucking-board  by  hammering  the  lead 
button  into  a  cube.  Pulverize  the  oxide  to  40  mesh  and  screen 
out  any  shot  lead.  Retain  the  powdered  litharge.  CAUTION: 
Avoid  breathing  poisonous  lead  fumes. 

g.  Re-read  this  entire  experiment  carefully,  and  be  sure  that 
you  understand  the  text,  have  performed  all  the  manipulations, 
and  can  answer  the  required  queries. 

h.  When  the  experiment  is  finished,  exhibit  the  data  and 
results  to  a  laboratory  officer.  If  it  is  satisfactory,  return 
the  special  apparatus  to  the  stock-room,  and  clean  up  your 
premises. 

Queries,  a.  Describe  and  explain  the  results  of  procedure 
b.  Write  an  equation  showing  the  reaction,  and  prove  your 
assumption  by  testing  the  products. 

b.  Describe  and  explain  the  results  of  procedure  c. 

c.  What  are  the  end  products  of  the  roasting  operation  c? 
Write  reactions  showing  how  each  was  formed.     Write  all  the 
reactions    performed    in  the  blowpipe  test  for  undecomposed 
sulfide. 

d.  Describe   the  experiment  with  zinc.     Why  should  zinc 
emit  copious  white  fumes  before  it  catches  on  fire?    What  is  the 


OXIDIZING  REACTIONS  17 

composition  of  these  fumes?  What  is  the  action  of  the  powdered 
coke  on  the  burning  zinc? 

e.  Describe  and  explain  the  appearance  of  the  scorifier  after 
procedure  /. 

/.  If  you  had  some  pig  iron  (essentially  an  alloy  of  iron  with 
from  2  to  5  per  cent  carbon)  and  treated  it  as  in  procedure  /, 
what  would  have  happened?  Give  cogent  reasons  for  your 
statements. 

g.  Had  the  iron  wire  weighed  3  oz.  and  25  per  cent  of  it 
been  converted  into  the  oxide,  how  many  B.t.u.  of  heat  would 
have  been  evolved?  How  many  grams  of  oxide  would  have 
been  formed? 

h.  How  many  cubic  feet  of  air  at  normal  conditions  will  be 
required  to  roast  i  Ib.  of  FeS2  completely  into  Fe20a  and  S02? 

i.  Describe  the  roasting  of  a  zinc  ore. 

j.  Describe  the  oxidized  ores  of  iron,  and  note  the  principal 
localities  in  which  they  are  produced. 


EXPERIMENT  NO.  3 
REDUCING  ATMOSPHERES  AND  REACTIONS 

Object.  The  object  of  this  experiment  is  to  reproduce  in 
the  laboratory  some  of  the  reducing  reactions  used  in  metallurgy. 

General  Explanation.  An  oxidizing  atmosphere  is  one  which 
contains  free  oxygen  (such  as  air)  or  contains  a  gas  which  can 
easily  furnish  oxygen  by  the  decomposition  of  its  molecule,  for 
example,  carbon  dioxide: 

C02-»CO+0-68,o4o. 

Such  an  atmosphere  will  give  up  oxygen  to  the  surrounding  sub- 
stances; the  intensity  of  the  oxidizing  reaction  varying  with  the 
temperature,  pressure,  and  relative  amount  of  the  reagents 
available. 

A  reducing  atmosphere,  on  the  contrary,  contains  an  excess 
of  gaseous  molecules  which  possess  an  "  affinity  "  for  oxygen; 
for  example,  acetylene  (C2H2),  carbon  monoxide  (CO),  or  a 
mixture  of  hydrocarbons  like  natural  gas.  Such  an  atmosphere 
tends  to  abstract  oxygen  or  similar  elements  from  the  substances 
it  surrounds;  the  reaction,  as  before,  varying  with  the  three 
conditions  mentioned. 

The  meaning  of  the  terms  oxidation  and  reduction  was  for- 
merly restricted  to  the  addition  or  subtraction,  respectively, 
of  oxygen  from  substances.  The  scope  of  the  words  has  now 
been  extended  to  include  the  addition  or  subtraction  of  other 
elements  (sulfur,  particularly),  or  the  raising  or  lowering  of  the 
valence  of  polyvalent  elements. 

The  third  type  of  atmosphere,  viz.,  the  neutral  atmosphere, 
is  one  which  has  neither  oxidizing  nor  reducing  effect,  as  these 
terms  have  been  denned.  In  the  laboratory,  pure  nitrogen 
furnishes  a  convenient  neutral  atmosphere,  for  it  is  an  extremely 

18 


REDUCING  ATMOSPHERES  AND   REACTIONS  19 

inert  gas  under  all  ordinary  circumstances.  In  commercial 
furnaces  a  neutral  atmosphere  is  ordinarily  a  mixture  of  oxidiz- 
ing and  reducing  gases  in  a  state  of  chemical  equilibrium  at  the 
existing  temperature;  the  state  is  one  of  balanced  activity  in 
which  the  oxidizing  effect  of  one  is  continually  undone  by  the 
reducing  action  of  another. 

The  mechanical  working  of  iron  and  steel  ingots  into  mer- 
chantable shapes  is  most  easily  done  at  high  temperatures. 
Even  those  special  operations  which  may  be  performed  cold, 
like  wiredrawing,  cold-rolling  and  pressing,  must  occasionally 
be  interrupted  by  a  heat  treatment  to  relieve  dangerous  internal 
stresses  and  to  restore  ductility  to  the  substance.  It  has  been 
shown  in  Experiment  No.  2  that  such  operations  in  the  open 
air  are  accompanied  by  the  formation  of  an  excessive  amount 
of  mill  scale  on  the  surface  of  the  piece,  the  relative  quantity 
of  which  increases  rapidly  with  the  decreasing  size  of  the  objects, 
because  the  ratio  of  superficies  to  mass  becomes  correspondingly 
larger.  Heating  and  annealing  furnaces  for  small  or  thin  articles 
must  therefore  operate  with  a  neutral  or  reducing  atmosphere. 

It  has  been  mentioned  that  most  ore  bodies  are  masses  of 
metallic  oxides  or  sulfides  mixed  with  a  variable  quantity  of 
barren  rock  materials  called  gangue.  The  minerals  containing 
the  valuable  metals  can  be  obtained  from  the  ore  in  a  relatively 
pure  state  by  mechanical  processes  called  "  concentration. " 
(See  Richards,  "  Ore  Dressing.")  Enormous  concentrating 
mills  employing  hundreds  of  men  and  treating  thousands  of 
tons  of  ore  every  day  are  in  operation  in  many  mining  centers. 
Leaving  out  of  consideration  at  this  time  the  treatment  of  any 
remaining  impurities  in  the  ore,  which  matter  will  be  the  sub- 
ject of  Experiment  No.  5,  the  commercial  production  of  the 
metal  from  oxides  and  sulfides  is  effected  by  reducing  reactions 
operated  on  a  grand  scale. 

Oxidized  ores,  either  found  in  nature  or  produced  by  roast- 
ing, are  in  most  cases  reduced  to  metal  in  the  "  blast  furnace." 
(See  Hofman,  "  General  Metallurgy,"  pp.  384,  475.)  This  is  a 
vertical  shaft  furnace  into  which  solid  ore,  flux,  and  fuel  are 


20  EXPERIMENTAL  GROUP  I 

charged  at  the  top.  Air  for  the  combustion  of  the  fuel  is  blown 
in  under  pressure  thru  openings  called  tuyeres  which  are 
located  in  the  walls  of  the  furnace  near  the  bottom.  The 
intense  heat  generated  at  this  zone  reduces  and  melts  the  metal 
in  the  ore,  which  is  tapped  molten  from  the  bottom  of  the  fur- 
nace. In  the  case  of  iron  oxide,  much  of  the  reduction  of  hema- 
tite is  accomplished  by  the  furnace  gases,  rich  in  carbon  monoxide 
ascending  thru  the  porous  column  of  descending  ore,  thus  * 


FeO+C-+Fe+CO-36,54o  (at  800°  C). 

In  copper  and  lead  blast  furnaces  the  charge  consists  quite 
generally  of  mixtures  of  oxides  and  sulfides,  which  react  upon 
each  other  as  follows: 


-  52,540. 

Any  surplus  of  oxide  may  be  reduced  by  the  carbon  in  the  fuel, 
thus: 

CuO  +  C  =  Cu  +€0-8540, 

altho  it  is  usual  to  provide  rather  a  large  excess  of  sulfides, 
which  will  melt  without  great  change.  This  alloy  of  metallic 
sulfides  will  collect  together  as  a  substance  called  "  matte," 
which  is  withdrawn  in  a  molten  condition  from  the  furnace, 
is  separated  from  slag  and  metal,  and  then  further  smelted  in 
machines  called  "  converters."  (See  Mills,  "  Materials  of  Con- 
struction," p.  552.) 

Special  Apparatus.    The  special  apparatus  needed  is  as  fol- 
lows: 

One  piece  of  f-in.  iron  pipe,  about  12  in.  long,  threaded. 

One  f-in.  gas  cock. 

One  o.i-gm.  trip  balance  and  weights. 

Spatula. 

One  button  brush. 

One  test  tube. 


See  Stoughton,  "  Metallurgy  of  Iron  and  Steel,"  p.  27. 


REDUCING  ATMOSPHERES  AND   REACTIONS  21 

Supplies.     The  supplies  needed  are  as  follows: 

One  piece  thin  iron  wire,  about  4o-gage,  16  in.  long. 

One  oooo  graphite  crucible. 

Twenty-five  gm.  hematite. 

Thirty  gm.  litharge. 

Twenty  gm.  copper  oxide  (CuO). 

Two  lo-gm.  clay  crucibles. 

Laboratory  Equipment.  The  laboratory  equipment  needed  is 
as  follows: 

Coke. 

Bucking-boards  and  mullers. 

Borax  glass. 

Galena. 

Salt. 

Covellite. 

Dilute  hydrochloric  acid. 

Procedure,  a.  Prepare  all  mixtures  before  starting  the  fur- 
nace, and  place  them  into  the  furnace  immediately  after  light- 
ing. Maintain  a  slightly  reducing  atmosphere  at  all  times, 
as  determined  by  Experiment  No.  i. 

b.  Sandpaper  the  thin  wire  until  it  is  bright,  twist  it  into  a 
spiral  around  a  pencil  and  insert  it  into  the  iron  tube.     Screw 
the  gas  cock  on  the  pipe  and  connect  to  a  gas  supply  with  a 
rubber  hose.     Fix  the  pipe  with  a  condenser  clamp  in  such  a 
manner  that  the  flames  from  the  lid  of  the  pot  furnace  will 
strongly  heat  that  part  which  contains  the  wire.     Pass  a  slow 
current  of  gas  thru  the  tube  during  the  entire  operation;   heat 
strongly  for  an  hour,  remove  the  pipe  from  the  flame,   and 
cool  without  shutting  off  the  gas  current.     CAUTION:    protect 
the  rubber  hose  from  the  heat. 

c.  Remove  the  wire  and  examine  it  critically,   comparing 
its  condition  to  that  of  a  short  untreated  piece  reserved  for  the 
purpose,  and  to  that'  of  the  oxidized  wire  from  Experiment  No.  2. 
Observe  the  color,  luster,  and  general  appearance.     Test  the 


22  EXPERIMENTAL  GROUP  I 

ductility  by  counting  the  number  of  times  it  must  be  bent  back 
and  forth  to  break  it.  Test  the  hardness  with  a  file.  Test  the 
magnetic  qualities  and  solubility  in  dilute  HC1  of  any  scale 
which  can  be  loosened.  Prepare  a  quenching  bath  by  filling 
a  pail  with  tap  water,  and  place  it  as  close  to  the  furnace  as 
possible.  Grasp  a  short  piece  of  the  original  wire  and  of  the  heat- 
treated  wire  side  by  side  in  the  jaws  of  a  small  tongs,  and  heat 
them  to  a  bright  red  in  the  reducing  flame  issuing  from  the  pot 
furnace.  Quench  the  wires  by  quickly  plunging  them  at  the 
high  heat  into  the  cold  water.  Speed  in  transfer  is  the  prime 
essential.  Test  both  pieces  as  before. 

d.  Make  up  a  charge  with  35  gm.  litharge  (PbO),  using  that 
made  in  Experiment  No.  2,  and  test  the  reducing  action  with 
galena  (PbS)  .     Pulverize  all  the  materials  to  40-mesh,  weigh  out 
the  required  amount  of  the  reagents,  add  about  2  gm.  of  fine 
coke,    mix    thoroly   by   rolling  together  on  a    rubber   mixing 
cloth,  and  place  the  charge  in  a  clay  crucible.     Fill  the  balance 
of  the  crucible  with  salt.     Heat  rapidly  from  the  cold  in  the  oven 
furnace,  remove  and  pour  into  a  button  mold  at  a  bright  red 
heat,  first  examining  the  melt  to  see  if  it  is  thoroly  molten. 
Examine  the  button  carefully,  break  the  metallic  lead  loose  with 
a  hammer,  brush  it  free  from  foreign  matter,  shape  it  into  a  cube 
with  a  hammer,  and  weigh.     CAUTION:     Always  wear  goggles 
when  examining  or  pouring  molten  materials.     Better  be  safe 
than  sorry. 

e.  Test  the  reactions 

2CuS+O2  =  Cu2S+SO2+69,36o; 

-  26,440. 


Covellite  (CuS)  on  being  heated  will  readily  break  down  into 
the  compound  Cu2S  which  will  then  react  with  the  copper  oxide. 
Figure  the  amount  of  Cu2S  necessary  to  reduce  the  oxide,  and 
then  figure  the  amount  of  covellite  required  to  produce  the  Cu2S 
according  to  the  first  equation.  Use  about  20  gm.  of  CuO. 
Thoroly  mix  the  pulverized  materials,  adding  about  2  gm. 


REDUCING  ATMOSPHERES  AND  REACTIONS  23 

pulverized  coke,  transfer  to  a  clay  crucible,  cover  with  salt,  heat 
strongly  in  the  pot  furnace,  and  pour  at  a  bright  white  heat. 
Separate  the  copper  and  weigh. 

/.  The  most  fusible  pig  iron  (alloy  of  95.7  per  cent  iron  with 
4.3  per  cent  carbon)  melts  at  1135°  C.,  while  pure  iron  melts 
at  1500°  C.,  a  temperature  beyond  the  capacity  of  the  gas  fur- 
naces. Hematite  can  be  reduced  by  coke  according  to  the  fol- 
lowing reaction: 

Fe2O3+3C— >  2Fe+3CO  — 108,120. 

The  infusible  iron  will  absorb  any  excess  of  carbon  existing 
in  its  neighborhood  and  be  converted  into  the  more  fusible  pig 
iron.  Therefore,  weigh  out  about  25  gm.  hematite,  and  a  com- 
puted amount  of  pulverized  coke  (thru  40  mesh)  to  effect 
the  reduction  according  to  the  above  equation,  together  with 
excess  of  coke  sufficient  to  form  the  most  fusible  pig  iron. 
Assume  the  coke  to  be  90  per  cent  carbon.  Then  add  approxi- 
mately 10  gm.  powdered  borax  glass,  and  mix  thoroly  by 
rolling  on  a  mixing  cloth.  Transfer  the  charge  to  a  oooo  graphite 
crucible,  and  cover  with  a  small  amount  of  borax  glass.  Heat 
from  the  cold  in  the  oven  furnace,  transfer  the  hot  crucible  quickly 
to  the  pot  furnace  after  pouring  e,  and  heat  for  thirty  minutes 
to  the  highest  temperature  attainable.  Pour  quickly  into  a 
button  mold,  and  carefully  remove  any  material  which  adheres 
to  the  crucible  with  a  sharp  knife.  Crush,  separate  the  iron 
from  the  glass  with  a  magnet,  and  weigh. 

g.  Re-read  this  entire  experiment  carefully,  and  be  sure 
that  you  understand  the  text,  have  performed  all  the  manipula- 
tions, and  can  answer  the  required  queries. 

h.  When  the  experiment  is  finished,  exhibit  the  data  and 
results  to  a  laboratory  officer.  If  it  is  satisfactory,  return 
the  special  apparatus  to  the  stock-room  and  clean  up  your 
premises. 

NOTE.  These  last  two  instructions  have  been  repeated 
in  Experiments  Nos.  i,  2,  and  3,  and  will  be  understood  as 


24  EXPERIMENTAL  GROUP  I 

appearing   at   the   end   of   each  future  day's  work,   even  tho 
they  do  not  again  appear  in  print. 

Queries,  a.  Tabulate  in  five  columns  the  results  of  pro- 
cedure b  and  c  with  the  iron  wire. 

b.  Make  up  a  neat  tabulation  of  the  results  of  procedure 
d,  e,  and  /,  showing  the  weights  of  the  reagents  used,  the  theo- 
retical weight  of  the  metal  to  be  recovered,  and  the  actual 
weight  found. 

c.  Discuss   the   causes   of    any   discrepancies   between    the 
theoretical  and  the  actual  weights  of  metal  recovered. 

d.  What  is  the  function  of  the  salt  in  procedure  d  and  e? 
Of  the  borax  in  /? 

e.  Do  you  get  any  matte  in  the  melt  for  copper?     How  do 
you  know? 

/.  Give  the  computations  for  procedure  /  in  full. 

g.  What  is  the  theory  of  valence?  State  some  experimental 
facts  which  are  satisfactorily  explained  by  this  theory. 

h.  What  is  the  pronunciation  of  tuyere?  of  gangue?  of 
matte? 

i.  Explain  the  differences  noted  in  the  condition  of  the 
iron  wire  before  and  after  annealing;  also  before  and  after 
quenching.  What  happens  during  these  operations? 

j.  How  many  cubic  feet  of  methane  (CH-i)  at  standard  condi- 
tions would  be  required  to  reduce  10  kg.  of  Cu2O  to  metal? 
How  much  heat  would  be  evolved  or  absorbed  during  the  process? 


EXPERIMENT  NO.  4 
REFRACTORIES 

Object.  The  object  of  this  experiment  is  to  study  the  prop- 
erties of  the  more  common  refractories. 

General  Explanation.  Since  a  large  proportion  of  metallurgi- 
cal operations  are  conducted  with  molten  materials  at  quite 
high  temperatures,  it  is  evident  that  the  containers  and  the 
furnaces  must  be  constructed  of  substances  which  will  with- 
stand such  extreme  heat  without  being  melted.  A  substance 
of  high -melting  point  is  said  to  be  a  "  refractory  "  material, 
and  bricks,  crucibles,  muffles,  and  other  shapes  made  of  it  are 
termed  "  refractories." 

Some  pure  substances  melt  at  temperatures  attained  in  the 
electric  arc  (3500°  C.db).  Graphite  (C),  calcium  oxide  (CaO), 
and  magnesia  (MgO)  are  common  instances.  Other  substances 
much  used  in  refractory  materials  melt  in  the  neighborhood  of 
2000°  C.;  such  are  alumina  (Al2Oa)  at  2000°  C.,  chromite 
(Fe2O3)x(Cr2O3)J/  at  2200°  C.,  fire-clay  (Al203)z(SiO2)z,  in  the 
region  of  1800°  C.,  silica  (SiO2)  at  1600°  C.,  and  carborundum 
(SiC)  which  dissociates  at  2250°  C. 

These  temperatures  are  for  the  most  part  approximations. 
The  difficulties  attending  such  measurements  may  be  realized 
when  it  is  known  that  the  melting-point  of  silica  has  been  var- 
iously reported  at  from  1200°  C.  to  2000^  C.  Very  pains- 
taking and  thoro  work  by  Day  and  Shepherd  (American 
Journal  of  Science,  1906,  p.  273)  shows  that  solid  silica  changes 
into  solid  tridymite  with  large  increase  in  volume  at  775°  C. 
±25°,  and  that  solid  tridymite  melts  into  an  extraordinarily 
viscous  liquid  at  1610°  €.±15°.  The  changes  take  place  very 
slowly;  the  just  molten  tridymite  can  only  be  distinguished 

25 


26  EXPERIMENTAL  GROUP  I 

from  the  just  solid  tridymite  by  microscopic  examination  under 
polarized  light.  As  a  matter  of  fact,  the  roofs  of  open-hearth 
furnaces  manufacturing  steel  are  made  of  silica  brick,  and  are 
steadily  run  for  weeks  at  temperatures  in  excess  of  1600°  C. 
without  failure  of  the  brickwork.  In  fact,  only  silica  brick, 
of  all  cheap  refractories,  possesses  the  required  compressive 
strength  at  such  high  temperatures  as  to  be  available  for  use  in 
the  construction  of  the  low-arched  roofs  of  these  steel  furnaces 
actually  working  at  a  higher  temperature  than  the  true  melting- 
point  of  the  brickwork  itself.  (See  Mills,  "  Materials  of  Con- 
struction," p.  389.) 

It  has  been  found  that  very  small  percentages  of  impurities 
will  lower  the  melting-point  of  these  refractories  to  a  marked 
degree,  even  tho  the  melting-point  of  the  impurity  be  higher 
than  that  of  the  refractory.  Thus,  a  little  lime  is  used  as  a  binder 
in  the  manufacture  of  silica  brick — pure  silica  having  no  cohesion 
in  itself  to  enable  it  to  retain  its  shape  after  molding.  But 
the  amount  of  lime  must  be  no  greater  than  absolutely  neces- 
sary in  order  to  prevent  harmful  effects  on  the  refractory  proper- 
ties of  the  brick  itself.  For  this  reason  it  is  evident  that  only 
the  purest  and  most  uniform  rocks  can  be  utilized  in  the  manu- 
facture of  all  refractories.  Of  course  other  properties  than  fusi- 
bility must  be  considered  in  the  choice  of  furnace  materials,  such 
as  its  coefficient  of  expansion,  strength  and  toughness  at  low  and 
high  temperatures,  behavior  under  rapid  change  in  temperature, 
and  conductivity  of  heat  and  electricity.  For  a  discussion  of 
such  features,  the  student  is  referred  to  Havard's  book  on 
"  Refractories  and  Furnaces." 

A  good  refractory  must  not  only  resist  the  action  of  the  heat, 
but  must  be  chemically  inactive;  that  is  to  say,  it  should  resist 
the  corrosion  of  any  liquid  material  with  which  it  may  be  in 
contact.  For  instance,  a  silica  or  fire-clay  brick  is  rapidly 
wasted  away  when  in  contact  with  a  slag  or  liquid  melt  con- 
taining a  large  percentage  of  lime.  This  slag,  however,  is  per- 
fectly resisted  by  a  magnesite  brick.  Such  facts  as  these  have 
led  to  the  following  classification: 


REFRACTORIES  27 

Name  of  refractory.  Composition. 

Basic:  Lime  CaO 

Dolomite  (CaO)(MgO) 

Magnesia  MgO 

Alundum  A^Os 

Bauxite  A1203 +#SiO2 

Neutral:  Chromite  Fe  and  Cr  oxides 

Graphite  C 

Carborundum  SiC 

Acid:  Fire-clay  (Al2O3)n(Si02)m 

Silica  SiO2 

A  magnesite  brick  typifies  the  basic  refractories,  a  silica 
brick,  the  acid;  and  chromite  is  neither.  It  will  be  noted  that 
the  prominent  basic  refractories — magnesia,  dolomite  and 
lime — are  made  of  the  alkaline  earth  oxides,  each  of  which  is  the 
anhydride  of  a  very  active  base.  On  the  other  hand,  the  most 
prominent  acid  refractory,  silica,  is  made  of  the  anhydride  of 
the  various  silicic  acids.  Hence  the  metallurgist  uses  the  same 
terms,  acid,  and  base,  as  are  used  in  elementary  chemistry. 
The  student  should  realize,  however,  that  the  ordinary  tests  for 
acid  and  base  cannot  be  applied  in  metallurgical  reactions. 
He  has  been  accustomed  to  distinguish  an  acid  from  a  base  by 
their  action  on  litmus  and  other  indicators  and  by  their  behavior 
during  electrolysis.  But  the  chemistry  of  aqueous  solution 
vanishes  at  temperatures  above  100°  C.,  and  the  best  the 
metallurgist  can  say  about  the  chemical  action  at  high  tempera- 
ture is  that  the  substance  which  is  a  base  in  aqueous  solution 
tends  to  act  as  a  base  at  high  temperatures,  and  that  the  acid 
of  aqueous  solutions  acts  as  an  acid  at  high  temperatures.  Bear 
in  mind  at  all  times,  however,  that  the  terms  acid  and  base  are 
relative  terms  only.  Thus,  iron  oxide  will  act  as  a  base  with  the 
very  acidic  silica  forming  iron  silicates,  but  will  act  as  an  acid 
with  the  very  basic  lime  forming  lime  ferrates.  Again,  bauxite 
brick  will  resist  corrosion  and  union  with  silica  to  a  very  high 


28  EXPERIMENTAL   GROUP  I 

temperature,  and  therefore  may  be  called  basic;  but  in  the  pres- 
ence of  lime,  easily  fusible  compounds  will  be  formed. 

As  an  example  of  the  use  of  such  refractories  take  the  case 
of  the  so-called  "  basic  open-hearth  furnace  "  (Mills,  "  Materials 
of  Construction,"  p.  387  et  seq.).  Given  the  fact  that  this 
process  operates  with  a  slag  containing  a  high  percentage  of 
lime,  then  the  lower  portion  of  the  furnace  must  evidently  be 
of  the  same  nature  as  the  slag  it  holds  in  order  to  resist  corrosion, 
and  consequently  is  made  with  magnesite  brick  side  walls  and 
granular  dolomite  hearth.  Magnesite  brick  has  not  the  mechan- 
ical strength  at  high  temperatures  to  permit  the  construction 
of  the  arched  furnace  top,  which  is  therefore  made  of  silica 
brick.  At  the  point  of  contact  of  these  two  different  kinds  of 
brick  a  parting  of  neutral  brick  must  evidently  be  placed  to 
prevent  the  rapid  formation  of  magnesium  silicates,  and  conse- 
quently a  "  neutral  "  course  of  chromite  brick  everywhere  sepa- 
rates the  two. 

Special  Apparatus.  The  special  apparatus  needed  is  as  fol- 
lows: 

Glass  stirring  rod. 

Stiff  wire  brush. 

One  loo-mesh  screen  and  pan. 

One  200  c.c.  glazed  porcelain  pestle  and  mortar. 

Fragment  of  2-in.  round  graphite  electrode. 

Hand- saw. 

o.i -gram  trip  balance  and  weights. 

Brass  mold  for  Seger  cones. 

Spatula. 

Supplies.     The  supplies  needed  are  as  follows: 

One  2oo-c.c.  beaker, 
loo-c.c.  of  cylinder  oil. 
25  c.c.  vaseline. 
Fragments  of  the  following  No.  i  refractories: 

Silica  brick.  Magnesite  brick. 

Bauxite  brick.  Fire-clay  brick. 


REFRACTORIES  29 

Laboratory  Equipment.     The  laboratory  equipment  needed 
is  as  follows: 

Bucking-board  and  muller. 

"  Hy-temp  "    or    other    electrical    resistance    furnace    with 

proper  electrical  control. 
Optical  pyrometer  to  read  1800°  C. 
Solid  reagents  in  suitable  containers: 


Alumina, 

Hematite,  Fe2O3 

Silica,  SiO2 

Kaolinite  (Al2O3)(SiO2)2 

Lime,  CaO,  freshly  burned. 

Procedure.  NOTE:  The  following  instructions  cover  the 
examination  of  relatively  pure  refractories,  such  as  are  used 
for  the  manufacture  of  first-class  fire-brick,  and  even  the  highest 
temperatures  will  show  little  if  any  effect  upon  the  Seger  cones. 
Various  squads,  therefore,  should  add  increasing  percentages 
of  flux  to  the  brick  during  the  grinding.  In  this  way  a  series 
of  experiments  can  be  exhibited  showing  the  effect  of  impuri- 
ties upon  the  softening  point  of  the  purer  refractory.  A  series 
of  additions  up  to  the  following  maxima  are  suggested  : 

For  silica  brick:     200  per  cent  A^Os  plus  5  per  cent  Fe2Os. 
For  bauxite  brick:    10  per  cent  SiO2  plus  10  per  cent  Fe2Os. 
For  magnesite  brick  :     20  per  cent  kaolinite. 
For  fire-clay  brick:    3  per  cent  CaO  plus  6  per  cent  Fe2Os. 

a.  Interview  the  instructor  to  find  the  amount  of  impuri- 
ties he  wishes  you  to  mix  with  the  pulverized  materials. 

b.  Heat  the  cylinder  oil  over  a  Bunsen  flame,  and  dissolve 
in  it  about  one  quarter  of  its  bulk  of  vaseline.     This  will  be 
used  as  a  binder. 

c.  Clean  the  bucking-board  and  screen  as  follows:     Brush 
the  bucking-board  and  muller  vigorously  with  the  wire  brush, 
covering  the  entire  surface  at  least  twice.     Take  several  frag- 


80  EXPERIMENTAL  GROUP  I 

ments  of  the  material  to  be  crushed,  and  grind  them  down,  using 
the  whole  surface  of  the  muller,  and  a  considerable  area  of  the 
bucking-board.  Brush  the  fines  into  the  sieve,  screen,  and  waste 
the  fine  materials.  Brush  off  the  board  and  muller  again  twice 
vigorously  with  the  wire  brush.  Clean  out  the  sieve  and  pan 
by  rubbing  with  the  fingers,  and  jarring  attached  particles 
loose. 

d.  Take  a  fragment  of  silica  brick,  weigh  it,  and  add  the 
necessary  amount  of  impurities  (if  any  is  prescribed  by  the  in- 
structor).     Pulverize    the   whole    until    it    completely    passes 
thru  the  loo-mesh  screen.    Avoid  spilling  the  fines  in  trans- 
ferring from  the  bucking-board  to  sieve,  and  vice  versa. 

e.  Thoroly    mix    this    powdered    material    in    the    mortar 
with  a  little  of  the  oil-vaseline  solution.    When  mixed  properly, 
with  the  correct  amount  of  binder,  the  powder  will  look  dry  and 
granular,  but  will  stick  together  readily  when  pressed  between 
the  fingers. 

/.  Mold  three  Seger  cones  by  tamping  this  granular  material 
into  a  clean  brass  mold.  A  good  cone  should  be  free  of  cracks, 
have  plane  sides,  and  a  sharp  point.  Place  these  cones  on  the 
clean  hearth  of  a  cold  oven  furnace. 

g.  Repeat  procedure  c  to  f  with  each  of  the  other  refrac- 
tories, bauxite,  magnesite,  and  fire-clay.  Be  particularly  care- 
ful to  clean  the  entire  equipment  thoroly  between  moldings, 
so  that  the  purity  of  the  mixtures  may  not  be  impaired. 

h.  When  all  the  cones  are  properly  made,  heat  the  furnace 
gradually  to  a  maximum  heat,  and  hold  at  this  temperature 
during  the  remainder  of  the  period.  Observe  the  temperature 
of  the  furnace  at  the  end  with  an  optical  pyrometer.  (See  Experi- 
ment No.  15.)  Cool  in  the  furnace. 

i.  On  the  following  day  examine  and  note  the  condition  of 
the  cones,  particularly  as  to  the  condition  of  the  tips.  Then 
select  the  best  and  sharpest  cone  of  each  class  for  further  experi- 
menting, reserving  the  others. 

j.  Saw  a  f-in.  wafer  from  a  2-in.  round  graphite  electrode. 
With  a  knife,  cut  the  squad-number  on  the  side  of  this  wafer, 


REFRACTORIES  31 

and  notches  in  one  surface  so  it  can  be  grasped  easily  by  small 
tongs  and  lowered  into  the  crucible  of  the  electrical  resistance 
furnace. 

k.  Place  the  four  cones  on  this  wafer  in  the  crucible  in  such  a 
manner  that  they  are  not  in  contact  with  their  surroundings. 
Then  close  the  furnace  and  gradually  raise  the  temperature 
to  1800°  C.,  carefully  maintaining  this  degree  as  nearly  constant 
as  possible  during  the  balance  of  the  period.  One  squad  member 
should  be  delegated  to  this  work,  while  others  proceed  to  the  next 
experiment.  The  furnace  tender  should  observe  the  temperature 
of  the  furnace  with  an  optical  pyrometer  at  fifteen-minute 
intervals,  and  make  the  necessary  electrical  adjustments  under 
the  advice  of  the  instructor. 

/.  On  the  following  day,  remove  the  cones,  examine  and  note 
their  condition.  Place  the  wafer  containing  the  cones  on  the 
designated  shelf  alongside  the  work  of  the  other  squads  for  pur- 
poses of  comparison.  Exhibit  here  also  one  of  the  cones  of  each 
kind  which  has  been  baked  in  the  muffle  furnace,  but  not  heated 
to  the  high  temperature.  This  will  serve  as  a  reference,  indica- 
ting the  original  condition  of  the  cones.  Also  attach  a  card 
giving  the  squad-number  and  personnel,  and  the  composition 
of  each  cone. 

Queries,  a.  Describe  the  results  of  the  various  squads, 
sketching  the  condition  of  representative  cones  after  exposure 
to  1800°  C. 

b.  Give  the  percentage  composition  of  each  refractory  when 
it  first  shows  appreciable  softening  at  1800°  C. 

c.  What  sort  of  brick  should  be  used  for  the  stack  of  an  iron 
blast   furnace?    For   the   bosh?     For   the   crucible?    For   the 
stoves? 

d.  Give  a  short  account  of  the  process  of  manufacture  of 
refractory  brick. 


EXPERIMENT  NO.  5 
SLAGS 

Object.  The  object  of  this  experiment  is  to  show  how  to 
produce  fusible  mixtures,  or  slags,  from  infusible  ore  substances, 
or  gangue,  and  to  show  the  effect  of  chemical  composition  upon 
the  properties  of  slags. 

General  Explanation.  In  the  smelting  of  ores,  the  operator 
must  recover  his  valuable  metal  in  as  pure  a  condition  as  possible. 
This  necessitates  the  separation  of  the  metal  from  any  impuri- 
ties which  may  be  present  in  the  ore.  Some  of  these  impurities 
may  be  volatile;  but  others  will  be  recognized  as  highly  refrac- 
tory and  would  scarcely  melt  before  the  furnace  itself.  Economy 
of  operation  demands  that  the  contents  be  removed  from  the  fur- 
nace in  the  fluid  state;  therefore,  the  problem  the  metallurgist 
must  face  is,  "  How  can  these  substances  be  smelted  into  a 
liquid  and  easily  fusible  slag?  " 

The  impurities  in  ores  are  of  widely  varying  composition 
and  character — their  general  nature  follows  that  of  the  barren 
"  country  rock  "  surrounding  the  mineralized  ore  body.  The 
gangue  of  an  ore  body  occurring  in  a  limestone  formation  would 
probably  be  high  in  limestone  (CaCOs),  and  therefore  basic 
(see  p.  27).  On  the  other  hand,  ores  in  igneous  rocks  would 
probably  be  very  high  in  silica  (SiO2),  and  therefore  acidic. 
In  many  ores,  valuable  metals  may  be  regarded  as  impurities; 
for  instance,  in  smelting  an  ore  for  copper,  the  iron  and  zinc 
content  is  slagged  and  thrown  away  with  the  other  impurities. 
This  is  necessary  because  of  the  fact  that  in  the  present  state  of 
metallurgical  art  there  is  no  method  known  for  saving  these 
valuable  metals  as  a  commercial  by-product. 

The  more  important  gangue  materials  of  various  ores  may 

32 


SLAGS  33 

be  listed  as  follows,  ranked  approximately  from  basic  to  most 
acidic : 

Basic 

Alkali  Na2O  and  K20 

Baryta  BaO 

Lime  CaO 

Magnesia  MgO 

Iron  oxide 
Manganese  oxide 
Alumina  A1203 

Boric  oxide  B2Os 

Titanium  oxide 
Silica  Si02 

Acidic 

As  noted  before  on  page  27,  acidity  and  basicity  are  relative 
terms;  for  instance,  alumina  acts  as  a  base  toward  substances 
below  it,  but  as  an  acid  toward  those  above.  This  property 
is  commonly  said  to  be  "  amphoteric." 

Silica  is  the  universal  acid  radical  in  rock  forming  minerals, 
and  practically  all  slags  contain  it  in  large  quantities;  for  this 
reason,  most  slags  may  be  termed  "  silicate  "  slags.  They  may 
also  contain  small  amounts  of  the  minor  acids,  such  as  P2Os, 
SO3,  Sb2Os,  As20s  and  TiO2.  The  basic  oxides  are  usually 
present  in  larger  variety — three  or  four  of  the  common  oxides 
are  ordinarily  present  in  considerable  quantity.  As  a  matter 
of  fact,  the  gangue  usually  does  not  contain  the  oxides  in  the  free 
state,  with  the  exception  of  quartz  (Si02),  but  the  ore  is  a 
mixture  of  minerals  of  definite  composition,  such  as  feld- 
spar (K^A^SieOie),  mica  (2KH-2MgFe-2AlFe-Si3Oi2),  calcite, 
CaCOs,  etc.  Chemical  analysis  of  the  ores  allows  one  to  separate 
the  constituent  oxides  in  the  manner  listed  above  before  making 
a  calculation  of  a  furnace  charge.  (See  Appendix  A.) 

In  order  to  remove  these  more  or  less  infusible  materials 
from  the  furnace  in  a  liquid  state,  one  avails  himself  of  the  facts 
covered  by  the  general  statement  that  "  Given  two  pure  sub- 


34 


EXPERIMENTAL  GROUP  I 


stances,  the  melting-point  of  either  is  lowered  by  the  addition 
of  certain  quantities  of  the  other."  The  logical  conclusion  of 
this  statement  is  that  there  must  be  one  or  more  mixtures  of 
lower  melting-point  than  either  of  the  constituents.  The  com- 
position of  the  mixtures  melting  at  the  lowest  points  does  not 
correspond  to  that  of  a  chemical  compound;  they  are  the  so-called 
"  eu  tec  tic  "  mixtures  appearing  under  the  microscope  as  an 


1512 


1500- 


1400 


1300 


1200 


1100 


1000 


aSiOa  Plus  Diopside 


Inversion  Points 


Diopside 


Inversion  Points 


Mixed     j 
Crystals  j 


of         I 


MgSiO  3 


I  Diopside  mixed 


la 
Diopside  I 


Crystal 


20 


40  60  80 

60  40  20  0 

FIG.  2. — Equilibrium  Diagram,  CaO-SiO^  :  MgO-SiQj. 
Reprinted  from  Hofman  "  General  Metallurgy,"  by  permission  of  the  McGraw-Hill  Book  Co. 

intimate  mixture  of  minute  crystals  of  two  different  substances. 
(Eutectic  means  "  easily  melting.") 

This  general  statement  holds  for  alloys  of  elements,  oxides, 
or  more  complex  compounds.  As  an  illustration,  wollastonite, 
CaOSiO2,  melts  at  1512°  C.,  enstatite,  MgOSi02  melts  at 
1524°  C.  However,  a  eutectic  consisting  of  27.5  per  cent  of 
MgOSiO2  and  72.5  per  cent  of  CaOSiO2  melts  at  1350°  C.,  and 
another  eutectic  of  67  per  cent  MgOSiO2  and  33  per  cent  CaOSiO2 
melts  at  1375°  C.  The  only  true  chemical  compound  formed  by 


SLAGS  35 

these  two  silicates  is  called  augite  (CaOMgO-2Si02),  and  it 
melts  at  1381°  C.,  lower  than  either  constituent,  but  higher 
than  either  eutectic.  (Hofman,  General  Metallurgy,  p.  444, 
shows  a  diagram  representing  the  melting-points  of  all  com- 
bination of  these  two  silicates,  which  is  reproduced  above, 
Fig.  2.) 

Quickly  cooled  slags  are  glasses,  or  solid  solutions  of  the 
oxides  composing  them  and  of  the  compounds  which  could  exist 
as  stable  substances  at  the  temperatures  in  question.  On  more 
slowly  cooling,  the  stable  compounds  tend  to  separate  out  of 
the  mother  liquor,  and  may  be  identified  by  the  expert  under 
microscopic  examination.  The  constitution  of  slags  containing 
several  different  oxides  is  therefore  extraordinarily  complex, 
and  to  a  large  extent  is  yet  unexplored  territory.  It  is  certain, 
however,  that  the  old  fashion  of  assuming  all  the  bases  to  range 
together  on  the  one  hand,  and  the  acids  joining  on  the  other  to 
make  one  complex  silicate  molecule,  is  based  upon  no  ground- 
work of  fact.  However  that  may  be,  it  is  nevertheless  conveni- 
ent to  say  that  the  problem  of  slag-making  usually  consists  of 
determining  the  proper  amount  of  basic  material  to  add  as  a  flux 
in  order  to  make  a  readily  fusible  compound,  or  eutectic  mixture, 
with  the  excess  of  acid  present  in  the  gangue  of  the  ore,  or  vice 
versa,  as  the  case  may  be.  What  the  relative  proportion  of  acid 
to  base  may  be,  and  which  oxides  shall  be  regarded  as  acids  and 
which  as  bases,  are  questions  ordinarily  answered  by  the  metal- 
lurgist on  the  basis  of  his  experience  obtained  in  the  management 
of  certain  furnaces.  Fortunately,  considerable  latitude  is  allow- 
able in  most  processes,  and  universal  agreement  or  scientific 
exactitude  is  therefore  not  necessary  since  a  furnace  will  take 
care  of  itself  and  smooth  out  its  own  irregularities  to  a  certain 
extent. 

Temperatures  which  are  moderate  for  metallurgical  furnaces 
are  not  obtainable  in  the  ordinary  gas  muffle,  and  therefore 
special  acids  and  bases,  too  expensive  to  use  in  bulk,  are  utilized 
in  the  laboratory  to  make  more  fusible  slags.  Some  of  these 
combinations  are  molded  into  the  familiar  Seger  cones  of  experi- 


36  EXPERIMENTAL   GROUP  I 

merit  No.  i,  p.  8.  Such  substances  as  bicarbonate  (NaHCOs), 
litharge  (PbO),  and  borax  glass  (Na2B4O?)  are  extensively  used 
as  fluxes  in  assaying. 

-  Special  Apparatus.     The  special  apparatus  needed  is  as  fol- 
lows: 

One  o.i-gm.  trip  balance  and  weights. 

Spatula. 

Supplies.     The  supplies  needed  are  as  follows: 

Three  scorifiers. 
Six  5-gm.  crucibles. 

Laboratory  Equipment.     The  laboratory  equipment  needed  is 
as  follows: 

Optical  pyrometer. 

Charcoal. 

Two  bucking-boards  and  mullers. 

Trays  of  reagents,  as  follows :    Bicarbonate. 

Litharge. 

Borax  glass. 

Hematite. 

Silica. 

Fresh  burned  lime. 

Fluorite. 

Procedure,     a.  Fill  separate  scorifiers  half  full  of  each  of  the 
following  substances:     * 

Laboratory  bases. 

I.  Bicarbonate  (NaHCO3). 
II.  Litharge  (PbO). 

Laboratory  acid: 

III.  Borax  glass  (Na2B407). 

Weigh  the  scorifier  and  bicarbonate  both  before  and  after  heat- 
ing, in  order  to  note  any  loss  in  weight. 


SLAGS  37 

b.  Compute  the  amounts  of  reagents  necessary  to  make  the 
following  monosilicate  slags  : 

IV.  2PbO+SiO2  =  (PbO)2(SiO2).     Use  10  gm.  SiO2. 
V.  Fe2O3  +  C  +  SiO2  =  (FeO)2SiO2  +  CO.    Use  8  gm.  SiO2. 

c.  Replace  half  the  iron  oxide  in  the  latter  by  the  more 
basic  and  more  fusible  alkali  Na2O,  thus:     (Use  6  gm.  SiO2.) 

VI.  4NaHCO3+Fe2O3  +  C  +  2SiO2 


d.  Replace  half  the  silica  by  the  more  fusible  boric  oxide; 
using  5  gm.  silica: 

VII.  Na2B4O7  +  2NaHCO3  +  SiO2  +  Fe2O3  +  C 

=  (Na2O)2(FeO)2SiO2-B4O6+H2O  +  2CO2  +  CO. 

NOTE:  In  all  the  above,  the  amount  of  the  various  ingre- 
dients should  be  computed  previous  to  the  laboratory  period, 
and  the  calculations  should  be  presented  for  inspection  at  the 
beginning  of  the  afternoon  before  preceding  with  the  weighing. 
Use  charcoal  for  the  carbon,  assuming  it  to  be  100  per  cent  pure. 
All  materials  should  be  pulverized  to  40  mesh,  carefully  weighed, 
thoroly  mixed,  and  each  mixture  placed  into  a  5-gm.  crucible, 
properly  marked. 

e.  Tne  most  fusible  lime-silica  mixture  contains  37  per  cent 
CaO  and  63  per  cent  SiO2.     Make  up  two  samples  of  this  mix- 
ture, each  containing  about  15  gm.  SiO2  and  add  to  one  approxi- 
mately 10  per  cent  of  pulverized  fluorite  (CaF2).     Mix  well  and 
place  in  separate  crucibles,  marking  them  VIII  and  IX. 

/.,  Range  these  containers  in  the  cold  muffle  according  to 
the  plan,  Fig.  3.  Heat  strongly  in  a  neutral  flame,  observing 
conditions  at  fifteen-minute  intervals  and  being  careful  not  to 
cool  the  furnace  by  keeping  the  front  door  open  too  long.  As 
the  contents  of  the  containers  become  thoroly  molten,  with- 
draw each  from  the  furnace  and  pour  into  a  button  mold,  observ- 
ing the  approximate  temperatures  from  the  color  of  the  muffle 


38 


EXPERIMENTAL  GROUP  I 


(Experiment  No.  i).  Upon  request,  a  laboratory  officer  will 
check  your  estimate  by  means  of  an  optical  pyrometer. 

CAUTION  :  Safety  goggles  must  be  worn  when  examining  and 
pouring  molten  material. 

g.  After  VII  is  removed,  close  and  drive  the  furnace  one 


Door^ 


FIG.  3. — Location  of  Slag  Containers  in  Oven  Furnace. 

hour  at  maximum  heat;  estimate  the  temperature,  remove  all 
the  remaining  crucibles,  and  examine  the  contents. 

h.  See  Procedure  h  and  i  of  Experiment  i.  It  is  important 
that  the  instructor  be  shown  all  melts  at  the  end  of  the  afternoon. 

Queries,  a.  Make  up  a  neat  tabulation  giving  the  following 
information:  Name  of  material,  chemical  formula,  weights  of 
materials  mixed,  color  before  heating,  color  after  heating,  melt- 


SLAGS  39 

ing-point,  viscosity,  general  appearance  and  condition  of  the 
slag,  general  appearance  and  condition  of  the  container. 

b.  Give  the  equation  for  the  formation  of  VI  and  the  detailed 
computations  for  this  mixture. 

c.  What  happens  to  I?     Compare  your  weighings  with  the 
theoretical  loss.     What  would  happen  should  water  be  added  to 
the  product? 

d.  What  is  the  result  of  adding  CaF2  to  a  calcium  silicate? 
Explain   this.     How   could   you   determine   whether   the   lime 
silicate  is  an  acidic  or  a  basic  slag? 

e.  Did  you  get  any  metal  from  melt  II?    Why  should  such 
metal  appear? 

/.  Give  reasons  for  any  corrosion  of  the  fire-clay  scorifiers  or 
crucibles. 

g.  What  would  be  the  composition  in  weight  per  cent  of  the 
slag  if  27  per  cent  of  the  number  of  basic  molecules  in  IV  were 
replaced  by  the  same  number  of  molecules  of  MgO? 


EXPERIMENTAL  GROUP  II 
FOREWORD  TO  THE  STUDENT 

The  experiments  of  Group  II  are  presented  in  an  effort  to 
acquaint  the  student  with  the  best  methods  of  measuring  accu- 
rately a  moderately  high  temperature.  A  very  large  part  of 
modern  metallurgical  progress  can  be  directly  attributed  to 
information  gained  by  a  study  of  the  behavior  of  pure  metals 
and  their  alloys  at  high  temperatures.  It  will  be  apparent  that 
any  investigations,  either  in  the  works  or  in  the  laboratory, 
must  be  predicated  on  strict  temperature  control. 

Experiments  Nos.  6,  7,  and  9,  will  therefore  indicate  practi- 
cal methods  whereby  excellent  pyrometers  may  be  easily  con- 
structed and  calibrated. 

Since  the  method  of  calibration  involves  the  determination 
of  the  melting-points  of  two  or  more  metals,  a  study  of  the  melt- 
ing-points of  various  binary  alloys  is  naturally  suggested  which 
will  directly  utilize  the  work  already  completed.  This  is  the  sub- 
ject matter  of  Experiments  Nos.  8  and  10,  the  latter  of  which 
constructs  an  equilibrium  diagram  of  the  simple  lead-antimony 
system.  This  family  of  alloys,  altho  of  small  commercial 
importance,  is  of  great  educational  value  since  all  the  members 
have  low  melting-points,  they  can  easily  be  handled  by  novices 
and  their  equilibria  throw  much  light  on  the  more  important 
and  complex  system  of  alloys  between  iron  and  carbon,  which 
includes  the  various  irons  and  steels. 


40 


EXPERIMENT  NO.  6 
THERMO-COUPLE  ELEMENTS 

Object.  The  object  of  this  experiment  is  to  study  the  action 
of  thermo-electricity  as  influenced  by  the  character  of  the 
metals  used. 

General  Explanation.  If  two  wires  of  different  chemical 
composition  or  physical  constitution  are  welded  together  at  one 
end  and  the  loose  ends  are  connected  to  a  sensitive  instrument 
capable  of  showing  a  small  electric  current,  a  current  will  be 
indicated  when  the  welded  junction  is  heated.  The  amount  of 
current  flowing  will  be  directly  proportional  to  the  electromotive 
force  maintained  by  the  heat  at  the  welded  ends;  and  inversely 
proportional  to  the  resistance  of  the  circuit.  This  statement 
follows  directly  from  Ohm's  law  that  the  ratio  between  the 
difference  of  electrical  potential,  or  electromotive  force  E,  exist- 
ing between  two  points  in  a  circuit,  and  the  current  C  produced 
thereby,  is  a  constant  and  equal  to  the  resistance  R  of  the  cir- 
cuit. In  symbols 

-  =  R 
Or,  transposing, 


In  the  case  under  discussion  the  resistance  of  the  circuit  will  be 
the  sum  of  the  resistance  of  the  two  wires  welded  together 
(elements),  the  connecting  wires  leading  to  the  electrical  meter, 
the  meter  itself,  and  the  various  contacts,  wire  to  wire. 

The  cause  of  this  current  is  primarily  due  to  the  phenomenon 
known    as    "  contact   electromotive   force."     If   two   disks   of 

41 


42  EXPERIMENTAL  GROUP  II 

unlike  metals,  such  as  zinc  and  copper,  are  placed  side  by  side 
and  a  positively  charged  plate  is  suspended  above,  the  plate 
will  deflect  toward  the  copper  as  soon  as  the  two  disks  are 
moved  together  so  that  they  touch  at  any  point.  The  contact  is 
a  source  of  electrical  energy  which  projects  positive  particles  of 
electricity  called  electrons  in  one  direction  and  negative  electrons 
in  the  opposite,  thus  charging  the  zinc  disk  with  positive  elec- 
tricity and  the  other  with  a  like  amount  of  negative.  The 
positive  charge  on  the  zinc  repels  the  like  charge  on  the  positively 
charged  plate  suspended  above,  while  the  negative  charge 
on  the  copper  attracts  the  plate,  the  result  being  as  noted— 
that  the  plate  swings  over  the  copper  disk. 

It  might  be  thought  that  the  electricity  on  the  zinc,  being 
at  a  higher  potential,  would  discharge  across  the  junction  to 
neutralize  a  like  amount  on  the  copper  plate  as  soon  as  a  second 
point  comes  in  contact.  The  flow  of  such  a  current,  however, 
would  give  an  instance  of  perpetual  motion,  evidently  an  absurd- 
ity when  it  is  considered  that  all  points  of  contact  between  the 
two  plates  are  alike  in  being  sources  of  electromotive  force, 
and  all  points  are  tending  to  keep  the  two  plates  at  a  different 
potential.  Each  point  in  contact  projects  electrons  like  every 
other  point  in  contact,  and  no  electrical  discharge  can  take 
place  across  this  generator. 

A  current  can  be  caused  to  flow,  however,  in  two  ways.  In 
the  first  place,  if  two  plates  of  unlike  metals  are  touched  at 
their  upper  ends,  and  the  lower  ends  immersed  in  a  solution  of 
certain  inorganic  substances,  a  current  will  be  produced.  Such 
a  current  is  not  an  instance  of  perpetual  motion,  however,  for 
a  certain  definite  quantity  of  chemical  energy  existing  in  the  sub- 
stances in  solution  is  transformed  into  electrical  energy  by  the 
degeneration  of  compounds  of  high  latent  heat  into  others  con- 
taining lower  amounts.  Currents  produced  in  this  manner  are 
the  cause  of  the  action  of  all  primary  electric  batteries  and 
probably  of  most  of  the  corrosion  of  iron  and  steel. 

In  the  second  place,  a  current  will  be  produced  from  a  source 
of  contact  electromotive  force  by  joining  the  ends  of  two  wires 


THERMO-COUPLE  ELEMENTS  43 

of  unlike  metals,  and  maintaining  a  difference  of  temperature 
between  the  two  junctions  of  the  wires  of  this  so-called  "  thermo- 
couple." Currents  such  as  these  are  the  basic  principle  under- 
lying the  action  of  most  instruments  for  the  measuring  of 
moderately  high  temperatures.  Such  instruments  are  called 
pyrometers.  The  value  of  the  contact  electromotive  force 
of  any  junction  varies  with  the  temperature,  and  can  therefore 
be  expressed  as  a  function  of  the  absolute  temperature  of  that 
junction;  therefore  the  measurement  of  the  electromotive 
force  (or  the  resistance  being  unchanged,  of  the  current  it 
induces),  by  suitable  electrical  instruments  gives  an  indication 
of  the  temperature  at  that  time  and  place. 

Peltier  found  that  if  a  current  of  electricity  be  passed  thru 
a  weld  of  two  metals,  such  as  copper  and  iron,  a  certain  quantity 
of  heat  is  absorbed,  or  a  like  amount  is  evolved  at  the  junction 
should  the  current  flow  from  the  copper  to  the  iron  or  vice  versa. 
This  fact,  known  as  the  "  Peltier  effect,"  furnishes  an  explanation 
of  the  phenomena  in  an  ordinary  thermo-couple.  If,  there- 
fore, a  circuit  is  composed  of  one  wire  of  copper  and  one  of  iron 
welded  together  at  the  ends,  a  current  flowing  past  one  junction 
from  the  copper  to  the  iron  will  absorb  a  certain  amount  of 
heat,  which  will  be  evolved  in  like  amount  at  the  other  junction 
where  the  current  flows  from  iron  to  copper.  Or,  without 
impressing  an  external  current,  if  a  difference  in  temperature 
be  maintained  at  these  two  welds,  the  circuit  will  act  as  a  heat 
engine,  absorb  heat  at  the  hot  junction  and,  transforming  it 
into  electrical  energy,  conduct  this  electricity  along  the  wires 
to  the  cold  junction,  and  there  reconvert  the  electric  energy 
into  heat,  which  is  evolved  at  that  point.  The  action  of  this 
engine  will  cool  off  the  region  of  the  hot  terminal  and  heat  the 
region  of  the  cold  until  both  arrive  at  the  same  temperature, 
at  which  time  the  contact  electromotive  force  at  the  two  junc- 
tions will  be  equal  and  opposite,  and  action  will  cease.  The 
energy  necessary  to  heat  the  fire  end  and  to  refrigerate  the  cold 
furnishes  the  work  necessary  to  maintain  the  existence  of  the 
electrical  current. 


44  EXPERIMENTAL  GROUP  II 

Naturally  the  amount  of  electrical  current  generated  will 
depend  upon  the  metallic  combination  as  well  as  upon  the  differ- 
ence of  temperature  between  the  hot  and  cold  ends.  The  value 
of  any  combination  for  use  as  a  thermo-couple  depends  upon 
several  other  characteristics  which  will  be  discussed  later,  but 
primarily  the  thermo-couple  should  produce  a  large  electromotive 
force,  and  therefore  a  proportionately  large  current  for  a  moderate 
difference  in  temperature  in  order  that  it  may  be  delicate  or 
sensitive. 

Several  different  combinations  of  metals  can  be  compared  by 
measuring  the  current  generated  when  the  ends  of  the  wires  are 
at  a  constant  difference  in  temperature.  The  easiest  way  to 
maintain  these  temperatures  is  to  immerse  the  welded  end  in 
boiling  sulfur,  while  the  other  ends  are  in  an  ice  bath. 

Special  Apparatus.     The  special  apparatus  used  is  as  follows: 

One  electrical  meter. 
One  retort  clamp. 
One  ring  stand. 

Various   wires,   i4-gage,    24  in.  long,   labeled  with  me- 
tallic tags  as  follows: 

Soft  iron. 

Music  wire  (hard). 

Music  wire  (annealed). 

Alloys  343,  183,  166, 

German  silver. 

Copper. 

Nickel. 

One  piece  of  lamp  cord,  24  in.  long. 
One  blast  burner. 

Supplies.    The  supplies  needed  are  as  follows: 

Ice. 

Twenty-five  gm.  sulfur. 
One  6-in.  by  i-in.  test  tube. 
One  f -in.  by  3-in.  test  tube. 


THERMO-COUPLE  ELEMENTS 

One  two-hole  cork  for  i-in.  test  tube. 
One  6-in.  piece  of  small  glass  tubing. 
One  piece  of  asbestos  paper,  2^  in.  by  36  in. 
One  piece  of  asbestos  paper,  6  in.  square. 


45 


Laboratory  Equipment, 
is  as  follows : 


The  laboratory  equipment  needed 


Spool  of  asbestos  string. 
Bare  arc,  with  proper  hood. 
Syrupy  sodium  silicate. 
Soldering  outfit,  including: 

Soldering  tool. 

Soldering  paste. 

Solder. 

Piece  of  cloth  for  wiping. 


FIG.  4. — Home-Made  Arc  Welder. 

Procedure,  a.  Make  up  a  thermo-couple  as  follows :  Polish 
both  ends  of  the  wires  with  emery  paper,  clamp  the  tip  ends  of 
two  wires  alongside  each  other  in  a  vise,  and  twist  them  tightly 
together,  two  or  three  turns.  Fuse  the  twisted  ends  by  bringing 


46  EXPERIMENTAL  GROUP  II 

them  slowly  down  to  the  flame  of  an  electric  arc,  which  may  be 
arranged  as  in  Fig.  4,  until  a  globule  of  molten  metal  forms  at  the 
tip.  Syrupy  sodium  silicate  makes  a  satisfactory  flux.  Always 
wear  darkened  goggles  and  look  thru  the  "noviweld"  glass  plate 
fixed  in  the  hood  to  protect  the  eyes  from  the  harmful  effect  of 
the  intense  light. 

b.  Solder   the   leads   to   the   couple   as   follows:     Heat   the 


FIG.  5. — Apparatus  for  Boiling  Point  of  Sulfur. 

soldering  tool,  plunge  it  into  the  soldering  paste,  wipe  off,  and 
rub  solder  over  the  end  of  the  heated  copper  nose  until  a  smooth 
bright  surface  results.  If  the  tool  is  too  hot  the  bright  so-called 
"  tinned  "  surface  oxidizes  and  becomes  dull  in  luster.  Clean 
and  "  tin  "  the  ends  of  the  wires  to  be  soldered  in  a  like  manner, 
twist  tightly  together,  and  fix  with  a  drop  of  solder. 


THERMO-COUPLE   ELEMENTS  47 

c.  Set  up  the  apparatus  as  shown  in  the  illustration  Fig.  5 
as  follows:     Wrap  the  strip  of  asbestos  paper  tightly  about  the 
large  test  tube,  covering  the  middle  part  of  its  length,  A.     Cut 
a  small  round  hole  in  the  center  of  the  square  piece  of  asbes- 
tos paper  B,  slip  it  over  the  lower  end  of  the  test-tube  to  act 
as  a  hood  over  the  flame,  and  hold  it  in  place  with  a  ring.     These 
precautions  are  to  insure  a  region  at  the  center  of  the  test-tube 
which  is  well  insulated  against  heat  transfer  so  it  will  main- 
tain constantly  the  temperature  of  boiling  sulfur.     The  cork  C 
in  the  top  is  to  prevent  the  vapor  catching  fire;   the  glass  tube 
D  is  required  to  prevent  an  increase  in  pressure  in  the  test-tube 
which  would  raise  the  boiling-point  and  then  burst  the  appara- 
tus.    The  small  test-tube  is  inserted  thru  the  cork  to  act  as 
a  protection  tube  for  the  thermo-couple  and  serves  to  prevent 
the  wires  from  sulfidizing. 

d.  Melt  the  sulfur  carefully,  using  only  enough  to  fill  the  tube 
for  3  cm.     Adjust  the  flame  so  that  the  vapor  rises  nearly  to  the 
top  of  the  test-tube,  where  it  condenses  and  runs  back  down  the 
sides.     A  point  in  the  center  of  these  fumes  will  now  be  main- 
tained at  the  boiling-point  of  sulfur,  444.7°  C. 

e.  Insulate  the  wires  from  one  another  at  the  welded  end 
by  running  a  "  figure  8  "  with  asbestos  string  for  about  6  in. 
Wrap  a  bit  of  asbestos  about  the  wires  to  form  a  cork  E  closing 
the  small  glass  protection  tube,  so  that  the  welded  end  is  at  the 
bottom.     Immerse  the  other  ends  in  the  ice  jar  F  and  connect 
the  free  ends  of  the  leads  to  the  binding  posts  on  the  meter, 
taking    particular    care    to    make    tight    connections.     Guard 
against  grounds  and  short  circuits. 

/.  Compare  all  wires  against  iron,  noting  the  needle  deflec- 
tion for  each  metallic  combination  to  one-tenth  unit.  Pay 
particular  attention  to  the  direction  in  which  the  current  is 
flowing. 

g.  Substitute  boiling  water  for  ice  in  the  pail  at  the  cold 
end  and  note  the  effect  on  the  thermo-couple  which  gave  the 
highest  reading. 

h.  Test  the  contact  electromotive  force  of  a  couple  made 


48  EXPERIMENTAL  GROUP  II 

from,   hard    and    annealed   music  wire.      Solder    the   junction 
instead  of  welding  in  this  instance. 

Queries,  a.  Make  a  neat  tabulation  arranging  the  metals 
and  alloys  tested  in  a  series  from  maximum  to  minimum  read- 
ing, showing  the  numerical  values  determined  by  the  meter. 
Such  a  list  might  read: 

Positive 

Zinc +6 

Lead +5 

Tin +2 

Iron o 

Copper —  i 

Silver —  5 

Gold -7 

Negative 

b.  What  is  meant  by  the  term  absolute  temperature?     Ex- 
press 329°  F.  in  absolute  temperature,  Centigrade. 

c.  Give   the  names   of   the  units  for   the  measurement  of 
electromotive    force,    resistance,    and    current.     Define    their 
magnitude. 

d.  Write  an  equation  showing  in  symbols  the  amount  of 
current  flowing  in  a  thermo-couple  and  its  attachments. 

e.  If  the  unit  on  the  meter  is  supposed  to  be  i  millivolt, 
what  current  would  flow  in  the  steel-german  silver  couple  if 
the  total  resistance  of  the  circuit  be  300  ohms?     Which  way 
does  the  current  flow? 

/.  Suppose  the  leads  were  lengthened  so  as  to  increase  the 
resistance  by  10  ohms.  What  would  the  current  then  be? 

g.  What  does  the  meter  actually  register,  current  or  electro- 
motive  force?  What  causes  the  needle  to  deflect — current  or 
electromotive  force?  Why  do  you  think  so? 


EXPERIMENT  NO.  7 
THERMO-COUPLE  CONSTRUCTION 

Object.  The  object  of  this  experiment  is  to  make  a  thermo- 
couple to  be  used  as  a  pyrometer  in  future  laboratory  investiga- 
tions. 

General  Explanation.  Note:  A  good  discussion  of  this 
subject  is  given  in  Chapter  IV  of  Burgess,  "  Measurement  of 
High  Temperatures." 

As  noted  in  Experiment  No.  6,  the  value  of  a  metallic  com- 
bination for  use  as  a  thermo-couple  depends  upon  several  char- 
acteristics, which  may  be  listed  as  follows: 

First,  the  thermo-couple  should  produce  a  high  electro- 
motive force  for  a  moderate  difference  in  temperature  in  order 
that  it  may  be  delicate  or  sensitive.  This  requirement  was 
investigated  in  Experiment  No.  6. 

Second,  the  wires  themselves  should  be  homogeneous,  so  that 
parasitic  currents  may  not  affect  the  accuracy  of  the  electrical 
indications.  Parasitic  currents  may  be  denned  as  those  uncon- 
trolled and  variable  electrical  effects  arising  from  any  one  of 
several  causes.  This  requirement  demands  wires  which  are 
perfectly  uniform  in  chemical  composition  thruout  their  length, 
and  are  free  from  hard  or  crystalline  spots  or  any  other 
variation  in  physical  constitution.  Wires  of  exactly  the  same 
chemical  composition  will  show  a  contact  electromotive  force 
should  they  possess  a  different  physical  structure.  This  fact 
was  demonstrated  in  Experiment  No.  6  where  a  thermo-couple 
made  of  hard  and  annealed  music  wire  was  tested  and  showed 
the  production  of  a  considerable  electrical  current.  The  soft- 
ened or  annealed  wire  was  made  from  the  hard  wire  by  merely 
heating  it  to  about  1000°  C.  and  then  slowly  cooling  it.  It  is 
important,  therefore,  that  couples  for  precision  work  should 

49 


50  EXPERIMENTAL  GROUP  II 

be  very  carefully  constructed  and  handled — a  mere  bending  of 
the  wire  may  produce  sufficient  "  cold- working  hardness " 
to  affect  the  accuracy  of  the  indication.  Such  hard  spots  are 
sources  of  parasitic  currents.  Wires  of  superior  quality  may 
be  had  from  the  Electric  Alloy  Company,  Morristown,  N.  J., 
and  may  be  tested  for  homogeneity  by  methods  described  by 
W.  P.  White,  in  the  "  Journal  of  the  American  Chemical 
Society,"  1914,  p.  2292. 

Third,  the  wires  should  be  stable  at  elevated  temperature, 
stable  chemically  and  stable  physically.  The  most  perfectly 
prepared  wire  would  rapidly  become  useless  if  it  oxidized  readily, 
or  alloyed  with  the  small  quantities  of  metallic  vapor  existing 
in  most  industrial  processes.  Physical  stability  requires  that 
crystalline  growth  at  the  high  temperatures  in  use  be  very 
slow.  Wires  which  change  suddenly  in  any  physical  property 
(that  is,  those  which  are  made  of  metals  possessing  "  allotropic 
transformations "  at  elevated  temperatures),  are  evidently 
not  stable  in  the  sense  here  used.  All  physical  properties  vary 
with  the  temperature — thus,  the  hardness  becomes  less  as  the 
temperature  increases,  the  specific  gravity  becomes  smaller 
with  rising  temperature,  and  so  on.  But  a  large  number  of 
metals  and  alloys  will  have  sudden  and  discontinuous  changes 
in  their  properties  at  certain  fixed  temperatures;  for  instance, 
pure  iron  loses  its  magnetism  suddenly  when  the  rising  tempera- 
ture passes  760°  C.  Evidently,  such  a  profound  rearrangement 
of  the  configuration  of  the  iron  molecule  as  to  cause  it  to  lose 
its  magnetism  will  doubtless  have  a  considerable  effect  upon 
such  a  property  as  contact  electromotive  force. 

Fourth,  the  wires  should  have  a  high  melting-point  in  order 
that  their  useful  range  may  be  as  extensive  as  possible. 

Fifth,  the  wires  should  not  be  so  expensive  as  to  prohibit 
their  common  use. 

Sixth,  the  wires  should  be  small  tho  rugged,  in  order 
that  the  temperature  of  the  hot  end  will  rapidly  attain  and 
closely  follow  that  of  the  surroundings  without  being  so  deli- 
cate as  to  require  gentle  handling. 


THERMO-COUPLE   CONSTRUCTION  51 

Considerations  such  as  these  point  to  the  fact  that  an  ideal 
thermo-couple  is  not  a  simple  matter  to  construct — indeed, 
has  not  yet  been  discovered.  The  best  couples  in  use  are  those 
of  pure  platinum  against  platinum  alloyed  with  10  per  cent  of 
rhodium  or  iridium.  These  platinum  couples  (ordinarily  desig- 
nated as  Pt — Rd  or  Pt — Ir)  are  sensitive,  homogeneous,  refrac- 
tory and  rugged,  but  have  the  disadvantage  of  being  very  ex- 
pensive. Again,  while  they  are  quite  stable  physically  at  high 
temperatures  and  resist  oxidation  perfectly,  they  are  rapidly 
destroyed  in  a  reducing  atmosphere  by  alloying  readily  with 
volatile  metals  and  metalloids  which  may  be  present.  It  is 
important  that  an  excess  of  oxygen  be  always  present  when  plati- 
num couples  are  in  use  in  order  that  any  volatile  substances 
may  be  readily  oxidized  and  thus  rendered  incapable  of  form- 
ing an  alloy. 

Altho  the  noble  metals  make  the  best  couples,  on  account 
of  the  high  cost  their  use  is  confined  to  scientific  investigations 
and  the  construction  of  standard  thermometers.  Cheap  couples 
for  use  in  commercial  practice  are  therefore  usually  made  of 
wires  of  base  metal  alloys.  Many  useful  couples  are  manu- 
factured of  alloys  whose  principal  metal  is  nickel  (melting- 
point  1450°  C.)  combined  with  various  percentages  of  chromium, 
iron,  copper,  manganese,  and  cobalt.  The  wires  furnished  for 
this  experiment  are  Hoskins'  Manufacturing  Company  nickel- 
chromium  alloys  Nos.  183  and  343,  i4-gage.  This  combination 
gives  a  high  electromotive  force.  The  wires  are  specially  made 
for  thermo-couple  use  and  are  homogeneous  in  constitution; 
they  resist  oxidation  up  to  1000°  C.  and  oxidize  but  slowly  at 
1100°  C. ;  the  wire  is  relatively  inexpensive;  the  gage  is  small 
enough  to  follow  a  rapid  change  in  temperature,  but  still  not  so 
small  as  to  become  rapidly  weakened  by  surface  oxidation. 

The  wires  composing  the  thermo-couple  must  evidently  be 
properly  insulated  from  one  another,  and  also  covered  carefully 
to  protect  them  from  the  corrosive  action  of  their  surroundings. 
In  case  the  couple  is  to  measure  the  temperature  of  a  bath  of 
metal,  the  protection  tube  is  necessary  to  prevent  the  wires  from 


52  EXPERIMENTAL  GROUP  II 

alloying  with  the  molten  metal.  The  protection  tube  must  in 
this  case  also  be  able  to  resist  the  corrosive  action  of  the  bath, 
in  order  that  it  may  not  be  rapidly  destroyed  and  at  the  same 
tune  vitiate  the  purity  of  the  melt.  Base  metal  wires  must 
further  be  protected  from  oxidation  or  sulfidation. 

Noble  metal  couples  have  very  small  quartz  tubes  or  beads 
strung  along  their  length  to  prevent  a  short  circuit  from  one  wire 
to  the  other  should  they  touch,  and  then  an  outer  tube  of  porce- 
lain or  quartz  covers  the  whole.  Quartz  has  a  very  low  coef- 
ficient of  expansion,  and  can  be  heated  or  quenched  very  rapidly 
— porcelain,  on  the  other  hand,  must  be  heated  and  cooled  with 
extreme  care.  Tubes  made  of  either  of  these  substances  are  quite 
brittle,  however.  Base  metal  tubes  should  not  be  used  for  noble 
couples  on  account  of  the  fact  that  metals  volatilize  to  a  minute 
extent  at  temperatures  below  their  melting-point,  and  this 
metallic  vapor  readily  alloys  with  the  superficies  of  the  thin 
elements  of  the  couple,  thus  destroying  the  chemical  homogeneity 
of  the  wires. 

It  is  often  difficult  to  procure  an  adequate  thermo-couple 
protection  tube.  Gillett  recommends  that  base  metal  couples 
may  be  insulated  from  the  harmful  effects  of  sulfur  fumes  by 
a  thin  glass  tube.  The  wires  can  be  protected  from  alloying 
with  a  lead,  aluminum,  antimony,  or  zinc  bath  by  closely  wrap- 
ping them  with  asbestos  string  and  then  covering  with  retort  or 
high  temperature  cement.  For  melts  of  copper  or  brass,  a 
nickel-lined  tube  of  siliconized  graphite  is  necessary.  An  iron 
protection  tube  can  be  used  in  a  lead  or  cool  aluminum  bath. 
A  common  arrangement  for  protecting  portable  couples  to  be  used 
about  the  works  to  measure  furnace  temperatures  is  made  by 
inserting  the  wires,  properly  separated  by  porcelain  or  quartz 
beads  into  a  seamless  protection  tube  of  nickel  or  steel,  screwed 
into  a  wooden  handle  which  also  contains  concealed  binding 
posts  for  joining  the  couple  to  wires  leading  to  the  electrical 
meter.  Such  tubes,  however,  are  rapidly  oxidized  under  most 
conditions,  and  their  replacement  often  amounts  to  quite  an 
expenditure./ 


THERMO-COUPLE   CONSTRUCTION  53 

In  laboratory  work  it  is  usually  possible  to  maintain  the  cold 
end  of  the  thermo-couple  at  a  constant  temperature  by  immersion 
in  an  ice  bath.  Manufacturers  of  pyrometers  have  adopted 
various  expedients  to  eliminate  the  necessary  correction  in 
portable  thermo-couples  where  the  cold  junction  is  at  a  variable 
temperature. 

Special  Apparatus.     The  special  apparatus  used  is  as  follows: 

One  electrical  meter. 
Supplies.     The  supplies  needed  are  as  follows: 

One  piece  of  Hoskins'  alloy  183,  24  in.  long. 
One  piece  of  Hoskins'  alloy  343,  24  in.  long. 
One  piece  of  lamp  cord,  24-in.  long. 
One  piece  of  okonite  tape,  12  in.  long. 
One  pint  pail  filled  with  kieselguhr. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Core  oven  at  100°  C. 
Bare  arc,  with  proper  hood. 
Syrupy  sodium  silicate. 
Spool  of  asbestos  string. 
Soldering  outfit,  including: 

Soldering  tool. 

Soldering  paste. 

Solder. 

Piece  of  cloth  for  wiping. 

Can  of  retort  cement. 

Carpenter's  hand-saw. 

Jig  saw. 

Brace  and  f-in.  bit. 

Piece  of  board,  ^  in.  by  6  in. 

Vise. 

Procedure,  a.  Weld  the  not  junction  as  instructed  in  Pro- 
cedure a  of  Experiment  No.  6,  or  in  the  electric  butt  welder  under 


54  EXPERIMENTAL  GROUP  II 

the  direction  of  a  laboratory  officer.     In  any  case,  present  the 
weld  for  inspection  before  proceeding. 

b.  Starting  about  18  in.  from  the  weld,  wrap  asbestos  string 
tightly   around   one   wire,    working   toward   the   weld.     When 
this  is  covered  as  close  up  to  the  joint  as  possible,  lay  the  bare 
wire  alongside,  and  continue  wrapping  out  to  the  bead  on  the 
weld.     Cover  the  bead  with  four  short  strings  put  on  cross- 
wise, the  ends  to  be  held  under  the  circular  wrapping.     Work 
back  from  the  weld,  covering  both  wires  for  a  distance  of  12  in.; 
then  the  bare  wire  separately  for  another  6  in. 

c.  Solder  the  lead  wires  to  the  thermo-couple  as  directed 
in  procedure  b  of  Experiment  No.  6.     Wrap  the  joint  tightly 
with  a  short  piece  of  electrician's  tape. 

d.  Connect  the  leads  to  a  meter,  and  heat  the  fire  end  gently 
in  a  gas  flame  to  test  for  a  possible  break  or  short  circuit.     During 
the  heating,  grasp  the  welded  end  and  the  soldered  connections 
in  pliers  and  work  gently  back  and  forth,  looking  for  any  oscilla- 
tion in  the  needle,  which  will  indicate  a  faulty  electrical  circuit. 

e.  Dampen  the  wrapping  and  rub  on  a  little  retort  cement, 
working  it  well  into  the  string  until  the  excess  cement  becomes 
somewhat   dry   and   granular.     Remove    this   excess,    dampen 
and  slick  over  the  insulation  with  a  little  water,  and  dry  slowly 
in  a  muffle  furnace  or  drying  oven  held  at  about  100°  C.     Put 
on  three  thin  coats  in  this  manner  and  lay  aside  to  dry  over 
night.     A  very  good  paste  for  filling  in  asbestos  string  is  sold 
by   the   Johns-Manville   Company   under   the   trade   name   of 
"  Retort  Cement."     The  Quigley  Furnace  Specialty  Company 
also  make  a  satisfactory  cement  called  "  Hytempite."     Hoskins 
recommends  a  mixture  of  10  parts  silica  thru  2oo-mesh  screen, 
2  parts  burnt  fire-clay  thru  2OO-mesh  screen,  5  parts  acid-free 
sodium  silicate,  mixed  with  hot  water  sufficient  to  make  into  a 
creamy  paste. 

/.  The  dried  couple  is  to  be  slowly  heated  from  cold  to 
bright  red  in  a  muffle  in  order  to  anneal  the  wire  and  properly  to 
bake  the  insulation. 

g.  Construct  an  ice  bath  by  packing  a  stout  glass  jar,  3  or 


THERMO-COUPLE  CONSTRUCTION  55 

4  in.  in  diameter,  into  a  pint  pail  with  some  insulating  ma- 
terial such  as  kieselguhr,  mineral  wool  or  asbestos  fiber.  Cut 
a  suitable  piece  of  wood  or  asbestos  lumber  to  serve  as  a  cover  to 
the  pail,  with  a  f-in.  hole  in  the  center  for  the  entrance  of  the 
wires. 

Queries,  a.  Define  the  words  "  metal  "  and  "  metalloid." 
Distinguish  between  the  terms  "  noble  metal  "  and  "  base  metal." 
List  several  chemical  elements  in  these  classes. 

b.  What  is  the  diameter  of  a  i4-gage  wire? 

c.  Why  is  it  necessary  to  keep  the  cold  end  at  o°  C.? 

d.  How  is  it  possible  to  arrange  a  couple  for  use  when  the 
cold  end  is  at  some  other  temperature  than  zero? 

e.  Would    lead    wire    make    a    satisfactory    thermo-couple 
element?     Why?     Would  iron?     Why? 


EXPERIMENT  NO.  8 
THE  COOLING  CURVE  OF  A  PURE  SUBSTANCE 

Object.  The  object  of  this  experiment  is  to  obtain  the 
cooling  curve  of  pure  lead. 

General  Explanation.  One  of  the  most  important  means  of 
investigating  the  properties  of  pure  metals  and  their  alloys  is  by 
an  examination  of  their  heating  and  cooling  curves.  Such  curves 
are  constructed  by  taking  a  small  portion  of  the  substance  to 
be  studied  and  observing  and  recording  the  temperature  of  the 
mass  at  uniform  intervals  of  time  during  a  uniform  heating  or 
cooling.  These  observations,  when  plotted  in  the  form  of  a  curve, 
will  show  whether  the  temperature  of  the  mass  rises  or  falls 
uniformly  with  the  continuous  addition  or  abstraction  of  heat. 

The  heat  which  a  body  absorbs  serves  either  to  raise  the  tem- 
perature of  the  mass  or  change  its  physical  condition.  That 
portion  of  the  heat  which  results  in  an  increase  in  temperature 
of  the  body  is  called  "  sensible  heat,"  inasmuch  as  such  a  gain 
in  heat  is  apparent  to  the  physical  senses  of  the  observer.  Precise 
calorimeter  experiments  have  revealed  the  fact  that  the  relation 
between  temperature  and  sensible  heat  can  be  expressed  by  a 
continuous  function  such  as 

H  =  (S+kt)t, 

where  H  is  the  total  heat  required  to  raise  the  temperature  from 

o°to*°, 

S  is  the  specific  heat  of  the  body  measured  at  o°, 
k  is  a  constant,  and 
/  is  the  final  temperature  of  the  body. 

56 


THE  COOLING  CURVE  OF  A  PURE  SUBSTANCE    57 

Evidently,  if  heat  were  supplied  to  the  body  at  a  uniform  rate, 
the  temperature  would  rise  continuously,  and  if  the  temperature 
were  plotted  against  time,  a  smooth  rising  curve  would  result. 
Or,  if  sensible  heat  were  abstracted  from  the  body  at  a  uniform 
rate,  a  time- temperature  curve  would  again  be  a  smooth  falling 
curve.  Such  a  curve  is  called  a  "  cooling  curve." 

However,  we  find  that  when  a  body  is  melting,  vaporizing, 
or  otherwise  suffering  an  abrupt  change  in  physical  properties, 
a  quantity  of  heat  is  absorbed  which  disappears  without  chang- 
ing the  temperature  of  the  body.  This  heat  absorbed  during  a 
change  of  state  is  called  "  latent  heat,"  because  it  is  transformed 
into  the  work  necessary  to  change  the  configuration  and  dis- 
position of  the  molecules  in  the  body ;  but  it  is  again  liberated  in 
equal  amount  when  the  reverse  change  takes  place.  The  latent 
heat  of  fusion,  for  instance,  is  the  heat  absorbed  by  the  work 
of  driving  the  molecules  far  enough  apart  so  that  the  necessary 
mobility  is  gained  to  change  the  body  from  a  solid  into  a  liquid; 
work  done  against  the  internal  forces  tending  to  hold  the  mole- 
cules more  rigidly  together  as  a  solid.  In  short,  it  is  the  heat 
required  to  change  a  hot  body  in  the  solid  state  into  a  hot  body 
at  the  same  temperature  but  in  the  liquid  state.  It  is  easy 
to  comprehend  that  these  large  latent  heats  will  notably  affect 
the  shape  of  a  cooling  curve. 

From  these  considerations  it  would  seem  that  should  the 
cooling  curve  be  continuous  and  smooth,  following  closely  a~ 
regular  course,  all  the  heat  abstracted  during  cooling  is  furnished 
at  the  expense  of  a  fall  in  temperature  of  the  body;  that  is  to 
say,  it  disappears  as  "  sensible  heat."  These  curves,  however, 
frequently  show  horizontal  portions  or  "  arrests  "  which  denote 
that  at  that  temperature  all  of  the  heat  constantly  radiating 
is  being  supplied  by  internal  changes  in  the  alloy  itself;  that  is, 
it  is  being  supplied  'by  the  evolution  of  a  certain  amount  of 
"  latent  heat." 

The  freezing  of  water  is  a  case  in  point  which  falls  within 
ordinary  experience.  Water  exposed  to  a  low  temperature  will 
radiate  heat  into  the  cold  atmosphere,  and  consequently  the 


58 


EXPERIMENTAL  GROUP  II 


temperature  of  the  water  will  steadily  drop  until  the  freezing- 
point,  o°  C.,  is  reached.  At  this  time,  despite  the  constant 
radiation  of  heat  into  the  colder  surroundings,  the  temperature 
remains  at  zero  until  all  the  water  is  changed  into  ice.  When  the 
whole  mass  is  entirely  solidified,  further  radiation  of  heat  is 
again  at  the  expense  of  the  sensible  heat  of  the  ice,  and  the 
temperature  again  falls  until  it  finally  arrives  at  the  low  tem- 
perature of  the  refrigerant.  During  the  solidification  period, 
however,  the  temperature  remains  stationary,  and  the  radia- 
tion is  at  the  expense  of  the  so-called  "  latent  heat  of  fusion  " 
of  the  ice,  which  equals  an  amount  of  heat  which  would 
raise  the  temperature  of  an  equal  amount  of  water  thru  an 
interval  of  80°  C. 

The  cooling  curve  of  liquid  lead  or  any  pure  metal  near  the 
solidification  point  is  entirely  analogous  to  that  traced  by  freez- 
ing water.  Let  a  properly  insulated  thermo-couple  be  immersed 
in  a  crucible  of  molten  lead  which  is  then  allowed  to  cool  in  still 
air,  and  the  reading  on  the  dial  recorded  every  thirty  seconds, 
as  follows: 


Time. 

Scale 
Reading. 

Time. 

Scale 
Reading. 

Time. 

Scale 
Reading. 

Min.       Sec. 

Min.      Sec. 

Min.       Sec. 

Beginning 

12.0 

4          3° 

5-4 

9 

4-8 

3«> 

10.7 

5 

5-4 

9          30 

4-2 

i 

9-5 

5         3° 

5-4 

IO 

3-6 

i        30 

8-5 

6 

5-4 

10        30 

3-0 

2 

7.6 

6         30 

5-4 

II 

2.6 

2            30 

6.9 

7 

5-4 

II        30 

2.1 

3 

6.2 

7         30 

5-4 

12 

1.8 

3         30 

5-7 

8 

5-4 

12            30 

i-5 

4 

5-5 

8         30 

5-2 

13 

1.2 

These  readings  will  appear  as  shown  in  Fig.  6  when  plotted 
on  cross-section  paper  as  ordinates  to  the  scale  of  i  unit=i  cm., 
against  times  as  abscissae  to  the  scale  of  i  minute  =  i  cm.,  and 
connected  with  a  smooth  curve.  Following  the  reasoning  given 
in  the  case  of  water,  we  know  that  during  the  time  4  min.  30 


THE  COOLING  CURVE  OF  A  PURE  SUBSTANCE 


59 


sec.  to  8  min.,  the  stationary  temperature  denotes  the  pro- 
gressive solidification  of  the  lead.  Therefore,  whatever  the 
temperature  of  the  other  readings  noted  may  signify,  we 
know  that  the  reading  5.4  corresponds  to  the  melting-point 
of  lead.  From  a  similar  series  of  observations  made  with  a 
mercury  or  air  thermometer,  the  melting-point  of  lead  has 
been  determined  to  be  327°  C.  In  this  instance  5.4  units  equals 


Milli  voltmeter  Readings  —  > 

M)  *.  OS  00  0  t*  Z 

°0 

°0 

\ 

• 

\ 

V 

niBQ,^ 

\ 

°oo 

\ 

°0 

1 

\ 

\ 

Fig.  7 
COOLING  CURVE 
OF  ANTIMONY 

X 

>-,,-< 

w>_ 

^s 

N 

Fig.  6 
COOLING  CURVE 
OF  LEAD 

^ 

\ 

N^ 

\ 

^ 

x 

1-1 


12 


10 


4              6              8             10 
Time  in  Minutes >• 


0     10     20     30    40 
Time  Intervals — 


FIGS.  6  and  7. — Cooling  Curves  of  Lead  and  Antimony. 

Special  Apparatus.     The  special  apparatus  used  is  as  follows: 

One  electrical  meter. 

One  oooo  graphite  crucible. 

Three  hundred  grams  pure  lead. 

Supplies.     The  supplies  needed  are  as  follows: 

Ice. 
Charcoal. 


60  EXPERIMENTAL  GROUP  II 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Bucking-board  and  muller. 

Procedure.  CAUTION:  New  graphite  crucibles  should  be 
heated  -very  slowly  the  first  time  they  are  used.  Rapid  heating 
will  expel  moisture  from  the  crucible  walls  so  rapidly  that  large 
pieces  of  graphite  will  be  flaked  away. 

a.  With  a  sharp  knife,  cut  the  letters  "  Pb  "  in  the  side  of  the 
crucible. 

b.  Melt  the  lead  slowly  in  a  pot  furnace,  and  when  it  is 
entirely  molten,  skim  off  any  floating  oxide  or  slag  with  a  splinter 
of  wood.     Then  fill  the  remainder  of  the  crucible  with  crushed 
charcoal.     Avoid    raising    the    temperature    much    above    the 
melting-point  of  the  lead  or  breathing  the  fumes  arising  from  the 
pot. 

c.  Place  the  cover  on  the  pot  furnace.     Slowly  heat  the  dried 
and  annealed  thermo-couple  constructed  in  Experiment  No.  7 
to  about  the   temperature  of  the  molten  lead  in  the  flames 
issuing  thru  the  opening  in  the  furnace  cover.     Lower  the  hot 
junction  into  the  center  of  the  melt,  holding  the  wires  in  position 
with  a  condenser  clamp  and  ring  stand. 

d.  Bend  the  thermo-couple  wires  so  that  the  cold  junction 
can  be  immersed  in  the  ice  bath   constructed  in  Experiment 
No.  7  and  connect  the  leads  to  the  electrical  meter.     Remove 
the  blast  lamp  as  soon  as  the  hot  junction  attains  the  tempera- 
ture of  the  bath. 

e.  Read  the  dial  on  the  meter  to  one-tenth  unit  at  fifteen 
second  intervals,  record  and  plot  the  observations  in  pencil,  as  in 
Fig.  7.     Continue    the  observations  to  about  two  units   below 
the  solidification  point.     After  each  reading,  the  meter  may  be 
tapped  gently  with  the  fingers  to  start  the  needle. 

/.  When  the  cooling  has  proceeded  far  enough,  make  sure 
that  the  couple  is  frozen  solidly  in  the  metal  by  attempting  to 
lift  it  out.  Then  light  the  blast  lamp  and  heat  the  crucible 
slowly  at  a  uniform  rate  until  the  lead  is  again  melted.  Read 


THE   COOLING   CURVE  OF  A   PURE   SUBSTANCE          61? 

the  meter  at  intervals  of  fifteen  seconds,  record  and  plot  the  heat- 
ing curve. 

g.  Shut  off  the  flame  and  observe  and  plot  another  cooling 
curve  according  to  procedure  e. 

h.  Present  curves  and  data  to  a  laboratory  officer  for  inspec- 
tion and  approval. 

i.  When  a  satisfactory  check  has  been  secured,  melt  the  couple 
free  from  the  bath,  allow  the  metal  to  cool  in  the  crucible,  remove 
the  crucible  from  the  furnace  and  return  it  to  the  stock  room. 
Melt  away  any  lead  adhering  to  the  insulation  by  holding  it  in 
the  flame  of  the  blast  lamp.  Cover  the  couple  with  a  fresh  layer 
of  cement,  and  lay  away  to  dry  over  night. 

Queries,  a.  Define  specific  heat.  What  is  the  unit  of 
heat? 

b.  The  specific  heat  of  a  cubic  meter  of  oxygen  is  as  follows: 

At       o°  C.  =  303  calories. 
200°  C.  =  314 
400°  C.  =  325 
6oo°C.=336 
8oo°C.=347 

Derive  a  formula  of  the  form 

Specific  heat  =  a+bt 

to  express  the  data  tabulated  above. 

c.  What  would  be  the  average  specific  heat  for  the  temperature 
interval  between  zero  and  1000°  C.? 

d.  How  much  heat  would  be  required  to  raise  5.3  cubic  meters 
of  oxygen  from  o°  C.  to  1000°  C.? 

e.  If  heat  were  supplied  to  i  cu.m.  of  oxygen  at  the  rate  of 
1000  calories  per  second,  plot  the  heating  curve  which  would 
result. 

/.  Discuss  the  reasons  why  the  heating  curve  of  lead  does  not 
give  as  satisfactory  results  as  a  cooling  curve. 

g.  Is  it  possible  to  cool  a  liquid  below  its  true  melting- 


62  EXPERIMENTAL  GROUP  II 

point?  Is  it  possible  to  heat  a  solid  above  its  true  melting- 
point  ? 

h.  Show  how  the  specific  heat  of  molten  and  solid  lead  can 
be  compared  by  a  cooling  curve.  Can  the  latent  heat  of  fusion 
be  computed  from  the  curve? 

i.  What  effect  would  a  small  quantity  of  alloying  impurity 
have  upon  the  melting-point  of  the  lead?  What  effect  would 
a  small  quantity  of  insoluble  impurity  have? 


EXPERIMENT  NO.  9 
THERMO-COUPLE  CALIBRATION 

Object.  The  object  of  this  experiment  is  to  calibrate  a 
thermo-couple  by  known  fusion  temperatures  of  metals. 

General  Explanation.  It  has  been  shown  in  Experiment 
No.  6  that  if  the  resistance  of  the  circuit  is  a  constant,  the 
amount  of  current  flowing  in  a  thermo-couple,  and  therefore  the 
indication  registered  on  the  dial  of  the  electrical  instrument, 
varies  directly  as  the  net  thermal  electromotive  force  generated 
in  the  couple.  This  resistance  is  very  nearly  constant  if  one  uses 
the  same  couple,  leads,  and  meter,  and  if  the  small  variation 
in  resistance  in  the  couple  wires,  due  to  varying  temperatures 
at  the  hot  junction,  may  be  disregarded.  The  net  electromotive 
force  of  the  couple  is  equal  to  the  contact  electromotive  force 
generated  at  the  hot  end  minus  that  generated  at  the  cold  end. 
In  symbols 

i.  R=ET-EC 

where  R  is  the  net  electromotive  force  of  the  couple,  ET  is  the 
contact  electromotive  force  generated  at  the  hot  end,  and  Ec 
is  the  contact  electromotive  force  generated  at  the  cold  end. 

It  was  also  stated  that  the  value  of  the  contact  electro- 
motive force  was  a  function  of  the  absolute  temperature,  that  is, 

II.  ET=f(T). 

HI.  Ec=f(C). 

where  T  or  C  is  the  absolute  temperature  of  the  hot  or  cold  end, 
respectively. 

63 


64  EXPERIMENTAL  GROUP  II 

Whence,  substituting  in  I, 
IV.  R=f(T)-f(Q. 

A  general  equation  which  exactly  expresses  the  relations  be- 
tween n+i  experimental  determinations  of  equal  accuracy  is 


.  .  .  AnTn 
and 

.  .  .  AC 


where  Ao,  AI,  A2,  AS  .  .  .  are  numerical  coefficients,  the 
same  in  both  expansions,  because  ET  is  the  same  function  of 
T  that  Ec  is  of  C. 

Substituting  in  Equation  IV  and  collecting 

V.    R  =  ET-EC  =  A1(T 


Now  substitute  for  the  absolute  temperatures  T  and  C  their 
equivalents  2+  273  and  £+273,  where  /  and  c  are  expressed  in 
the  ordinary  centigrade  scale.  Expanding  after  this  sub- 
stitution, and  collecting  like  powers  of  the  variables  /  and  c, 

VI.     ^  =  /-  ' 


It  will  be  noticed  that  the  quantities  multiplying  the  terms 
(/—  c)-,  (t2  —  c2)  .  .  .  consist  of  numerical  values  only,  whose 
sums  can  be  replaced  by  other  constants  such  as  p,  q,  r.  .  .  . 
This  is  really  to  be  expected,  inasmuch  as  the  substitution  of 
c+273  for  C,  etc.,  merely  shifts  the  origin  of  coordinates  273 
units  to  the  right,  and  the  degree  and  form  of  the  equation  is 
unaffected  by  such  an  operation,  as  is  well  known  from  analytical 
geometry.  Equation  VI  then  becomes 

VII.       R  =     t 


THERMO-COUPLE   CALIBRATION  65 

In  laboratory  work  the  cold  end  is  kept  in  an  ice  bath, 
whence  c  =  o,  and 

VIII.     R  =  pt+qt2+rP+st*  +  .  .  .     (cold  end  at  zero). 

As  a  matter  of  fact,  calibration  curves  of  useful  metallic 
combinations  are  so  flat  as  to  approach  a  straight  line — that  is, 
the  coefficient  q  is  very  small,  and  r  and  s  approach  zero.  For 
commercial  calibration,  therefore,  the  equation 

IX  R  =  pt+qt2     (cold  end  at  zero) 

will  be  found  to  express  the  relation  between  the  electro- 
motive force  registered  and  the  temperature  with  much  more 
precision  than  is  attained  under  the  conditions  of  subsequent 
use. 

Evidently,  then,  all  that  is  needed  to  calibrate  a  thermo- 
couple is  to  discover  the  numerical  value  of  the  constants  p  and 
q  in  equation  IX,  when  the  readings  corresponding  to  100°  C., 
200°  C.,  300°  C.  .  .  .  up  to  the  limiting  temperature  can  be 
computed,  plotted  to  scale  on  coordinate  paper,  and  the  points 
connected  by  a  smooth  curve.  This  curve  will  show  the  tem- 
perature in  degrees  Centigrade  corresponding  to  any  observed 
reading  on  the  dial;  or  vice  versa,  the  dial  reading  for  any  desired 
temperature. 

In  practice,  p  and  q  may  be  evaluated  by  a  pair  of  experi- 
ments which  determine  the  reading  on  the  dial  when  the  hot 
end  of  the  couple  is  plunged  into  a  pure  metal  or  salt  at  its 
melting-point.  The  exact  reading  on  the  dial  corresponding  to 
this  temperature  is  determined  from  a  study  of  the  cooling  curve 
of  the  metal  as  discussed  fully  in  Experiment  No.  8.  The  sub- 
stances chosen  for  the  calibration  should  have  melting-points 
near  the  ends  of  the  expected  useful  range,  with  a  third  selected 
midway  for  a  check.  A  list  of  standard  points  follows,  and  is 
taken  from  page  456,  Burgess's  "  Measurement  of  High  Tem- 
peratures." 


66 


EXPERIMENTAL  GROUP  II 


Substance. 

Boiling-point. 

Freezing-  point. 

Water.              

IOO 

Zero 

Naphthalene. 

218 

Tin 

27T     Q 

Benzophenone  

306 

Lead                                   

•?27 

Zinc 

A.IQ 

Sulfur    .        

444-  7 

Antimony                              

6*1 

Sodium  chloride 

800 

Silver  

06  1 

CoDDer. 

1083 

Lithium  metasilicate 

I2O2     • 

Diopside  

I  3QI 

Nickel                                

I4.CO 

Palladium 

I  ^  CO 

Platinum.  ...            

I7CC 

For  the  purpose  of  this  experiment,  pure  lead  and  common 
salt  (NaCl),  will  be  used  to  determine  the  coefficients  p  and  q. 
The  cooling  curve  of  lead  already  determined  in  Experiment 
No.  8  will  give  one  set  of  data,  while  a  corresponding  cooling 
curve  of  salt  gives  the  relation,  in  this  hypothetical  instance, 
of  12.8  units  =  800°  C. 

Two  independent  relations  between  the  meter  reading  and  a 
fixed  temperature  have  been  discovered  in  this  manner.  These 
values  substituted  in  Equation  IX  will  give 

For  lead,       5-4  =  />(327)+?(3272); 
For  salt,      i2.8  =  X8oo)+?(8oo2); 

which  gives  a  pair  of  simultaneous  equations  in  p  and  q.  Solv- 
ing, the  values  ^=+0.0169  and  c=  -0.00000115  are  found, 
and  the  equation  of  the  calibration  curve  for  this  particular 
couple  is  completely  determined  as 

^  =  o.oi69/— O.OOOOOH5/2. 

Values  of  R  can  now  be  calculated  for  each  hundred  degrees 
interval  from  this  equation,  and  plotted  as  illustrated  in  Fig.  8. 


THERMO-COUPLE   CALIBRATION 


67 


Special   Apparatus.     The    special   apparatus   needed   is   as 
follows: 

One  electrical  meter. 

One  oooo  graphite  crucible. 

One  sound  lo-gm.  clay  crucible. 

Three  hundred  grams  pure  salt. 

Three  hundred  grams  pure  antimony. 


ioooc 

900' 

CALIBRATION  CURVE 
FOR 
THERMO-COUPLE  NO.  13 

ALLOYS  183-343                       METER  7 

C-  C"    <^7/lAA/yrL/ 

x 

X 

800° 

X 

700° 

/ 

x 

600° 

X 

*1r 

500° 

x 

x 

400° 

,-X 

X 

300° 

X 

X 

E.juatiom-R  =  0.0169T-  .OOOOOllST^ 
Points  used:-  Pb  =32?°C.  =  5.4  Mv. 
Sb  =G31°C.=10.2Mv. 
Cheek  :-  S  =  444.?°C. 
Figures  7.  3  Mv. 
Reads     7.2  Mv. 

200° 

/ 

X 

100° 

X 

^^ 

x 

x 

04 

* 

«0 

00 

o 

OJ 

•** 

2 

Mill!  voltmeter  Readings >• 

FIG.  8. — Calibration  Curve  of  Thermo-Couple. 

Supplies.     The  supplies  needed  are  as  follows: 

Ice. 
Charcoal. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Bucking-board  and  muller. 

Procedure,  a.  With  a  sharp  knife,  cut  the  letters  "  Sb  " 
in  the  side  of  the  graphite  crucible  containing  the  anti- 
mony. 


68  EXPERIMENTAL  GROUP  II 

b.  Melt  the  salt  contained  in  the  clay  crucible  slowly  in  a 
pot  furnace,  but  avoid  heating  the  crucible  much  above  the 
melting-point  of  the  salt.     At  high  temperatures  the  material 
readily  volatilizes  and  is  so  labile  as  to  easily  work  its  way 
thru  checks  in  the  crucible  walls. 

c.  Follow  procedure  c  to  h  inclusive  of  Experiment   No.  8, 
taking  care  not  to  cool  the  crucible  more  than  100°  below  the 
solidification  point  of  the  salt,  until  the  work  has  been  inspected 
and  accepted.     Subdivide  the  duties  among  the  squad  and  plot 
the  cooling  curve  as  in  d  below. 

d.  Follow  procedure  b  to  i  inclusive  of  Experiment  No.  8 
with  the  crucible  of  antimony,   and  plot  as   shown  in  Fig.   7, 
p.  59,  where   the   time   scale   has   been   contracted.     In   such 
a    plot    it    is    unnecessary    and    undesirable    to    connect    the 
points  by  a  curve,  as  the  points  themselves  indicate  its  course 
excellently  well.     A  pencil  dot  is  even  better  than  the  small 
circle.     In  this  work  assign  one  member  of  the  squad  to  read 
the  meter,  another  to  call  time  intervals  and  record  the  read- 
ings, the  third  to  plot  the  readings  as  they  are  read  with  a  pencil 
on  cross-section  paper  (Fig.  7,  p.  59),  and  the  fourth  to  attend 
the  furnace  and  thermo-couple. 

Queries,  a.  Compute  the  values  of  the  coefficients  p  and  q 
in  Equation  IX  for  your  thermo-couple,  using  the  values 
obtained  by  the  melting-points  of  lead  and  salt.  Write 
the  equation  of  the  calibration  curve  as  an  explicit  function 

otR. 

b.  Using  this  equation,  compute  the  reading  for  the  melt- 
ing-point of  antimony. 

c.  Transform  the  equation  of  the  calibration  curve  into  an 
explicit    function   of  /.     Check    the  value   obtained    in  query 
b  by  means  of  this  equation.     It  should  agree  with  the  reading 
obtained  in  procedure  d  within  the  least  count  of  the  meter 
dial. 

d.  Compute  values  of  R  for  each  hundred  degrees,  and  draw 
a  calibration  curve  with  India  ink,  following  closely  the  style 
and  form  of  Fig.  8. 


THERMO-COUPLE  CALIBRATION  69 

e.  What  would  be  the  reading  on  the  meter  if  the  hot  end 
were  at  900°  C.  and  the  cold  end  in  boiling  water? 

/.  If  the  temperature  of  the  cold  end  were  disregarded, 
what  would  be  the  apparent  temperature  indicated  in  e? 

g.  What  is  the  cause  of  the  "  supercooling  "  effect  noticed 
in  the.  antimony  curve?  How  can  it  be  prevented? 


EXPERIMENT  NO.  10 
LEAD-ANTIMONY  ALLOYS 

Object.  The  object  of  this  experiment  is  to  construct  the 
equilibrium  diagram  of  the  lead-antimony  system. 

General  Explanation.  (Notes  on  the  commercial  importance 
of  these  alloys  may  be  found  in  Gulliver's  "  Metallic  Alloys," 
pp.  46  and  47.) 

Several  different  lead-antimony  alloys  can  be  melted  and 
their  cooling  curves  obtained  as  in  Experiment  No.  8.  These 
alloys  may  vary  in  composition  from  pure  lead  containing  no 
antimony,  thru  alloys  of  lead  containing  increasing  amounts 
of  antimony  up  to  the  limit  represented  by  pure  antimony  itself. 
As  we  have  already  noted  (p.  57),  a  sudden  discontinuity  or 
"  arrest "  in  these  cooling  curves  is  evidence  that  a  considerable 
proportion  of  the  constantly  radiating  energy  is  supplied  by 
latent  (not  sensible)  heat.  This  heat  may  be  produced  by  any 
one  of  a  variety  of  physical  or  chemical  changes  in  the  body  under 
observation;  and  a  complete  study  of  an  alloy  system  involves, 
among  other  things,  the  location  and  explanation  of  all  changes 
in  the  state  of  all  possible  alloys  in  that  series.  The  relations 
between  temperature,  composition,  and  constitution  obtained 
in  such  a  study  can  be  represented  graphically  upon  coordinate 
paper  in  what  is  called  an  "  equilibrium  diagram." 

The  equilibrium  conditions  of  the  lead-antimony  series 
may  be  simplified  by  a  consideration  of  the  cooling  curves  of  a 
series  of  solutions  of  ordinary  table  salt,  NaCl,  in  water.  We 
will  call  this  series  of  alloys  the  water-salt  system.  These 
two  systems  are  typical  of  an  important  and  common  family 
of  alloys  alike  in  that  the  components — lead  and  antimony 
or  water  and  salt,  respectively — form  no  compounds  with  each 

70 


LEAD-ANTIMONY  ALLOYS  71 

other,  and  are  perfectly  soluble  in  the  liquid  state  but  totally 
insoluble  in  the  solid.  In  other  words,  lead  and  antimony 
(or  water  and  salt)  alloy  perfectly  when  liquid,  but  upon  solid- 
ification, separate  into  a  cemented  mixture  of  minute  crystals 
of  pure  lead  and  of  pure  antimony  (or  pure  water  and  pure  salt). 

The  cooling  curve  of  pure  water  will  give  a  horizontal  arrest 
at  o°  C.  corresponding  to  the  freezing  of  water  into  ice.  A 
cooling  curve  of  a  solution  consisting  of  10  per  cent  salt  and 
90  per  cent  water  will  show  the  first  break  not  at  o°  C.,  but  at 
—4°  C.  This  arrest  is  not  a  horizontal  portion  of  a  curve  as  is  the 
case  in  a  pure  substance  (Experiment  No.  8),  but  merely  a  change 
in  the  direction.  Inspection  of  the  solution  shows  at  this  same 
instant  the  appearance  of  the  first  minute  crystals  of  solid, 
and  therefore  this  change  in  direction  of  the  cooling  curve  is 
interpreted  to  mean  that  at  that  instant  and  thereafter  only  a 
part  of  the  radiating  heat  is  furnished  by  the  sensible  heat  of 
the  mass,  and  the  balance  is  furnished  at  the  expense  of  the 
latent  heat  of  fusion  of  the  solidifying  substance. 

In  fact,  the  mass  does  not  solidify  at  a  constant  temperature; 
but  at— 4°  C.  the  first  few  crystals  separate  out  of  the  liquid, 
and  prove  on  analysis  to  consist  of  pure  water  in  the  form  of 
ice.  The  presence  of  the  salt  in  the  solution  has  evidently 
lowered  the  freezing-point  of  the  water.  This  phenomenon 
might  have  been  predicted  from  the  generalization  stated  in 
Experiment  No.  5:  "  Given  two  pure  substances,  the  melting- 
point  of  either  is  lowered  by  the  addition  of  certain  quantities 
of  the  other. " 

Within  limits,  the  amount  of  this  depression  of  the  freezing- 
point  varies  directly  with  the  amount  of  salt  in  the  solution. 
As  the  first  crystals  of  pure  water  form,  there  remains  behind 
a  liquid  (mother  liquor)  which  possesses  a  correspondingly 
less  amount  of  liquid  water,  and  therefore  contains  a  higher 
percentage  of  salt.  Consequently  the  freezing-point  of  this 
richer  salt  solution  is  lower  than  that  of  the  original,  and  other 
crystals  of  ice  cannot  separate  out  until  further  cooling  lowers 
the  sensible  temperature  of  the  entire  mass  to  the  freezing- 


72  EXPERIMENTAL  GROUP  II 

point  of  this  more  concentrated  salt  solution.  By  the  selective 
solidification  of  the  water  (and  consequent  removal  of  these 
crystals  of  water  from  the  liquid)  the  residual  mother  liquor 
becomes  richer  and  richer  in  salt,  and  the  temperature  at  which 
crystallization  takes  place  falls  further  and  further.  There 
must  be  a  limit  to  this  short  of  producing  pure  salt,  for  salt 
solidifies  at  800°  C.  This  limit  may  be  considered  as  being 
the  true  "  saturated  "  solution,  and  is  finally  reached  at  the 
temperature  of  —22°  C.,  when  the  whole  remaining  liquid 
solidifies  at  a  constant  temperature,  and  this  fact  is  shown  on 
the  cooling  curve  by  a  horizontal  portion. 

Should  the  ice  crystals  forming  from  such  a  solution  be 
removed  as  rapidly  as  they  freeze,  the  remaining  mother  liquor 
which  solidifies  as  a  pure  substance  would  be  found  on  analysis 
to  consist  of  23.5  per  cent  salt  and  76.5  per  cent  water. 

Other  salt  concentrations  will  produce  similar  freezing 
curves.  Assume  the  solution  to  be  15  per  cent  salt  and  85  per 
cent  water;  the  process  is  strictly  analogous,  except  that  the 
first  ice  crystals  freeze  out  at  a  still  lower  temperature  (about 
—  9°  C.);  which,  indeed,  is  to  be  expected.  The  solution  re- 
maining liquid  to  the  last,  left  behind  by  the  solidification  of 
more  and  more  water,  congeals  as  before  at  the  constant  tempera- 
ture of  —22°  C.,  and  possesses  the  same  composition,  i.e.,  23.5 
per  cent  salt  and  76.5  per  cent  water. 

If  a  solution  originally  possess  this  limiting  composition,  it 
has  only  one  freezing-point,  which  is  at  —22°  C.  This  cooling 
curve  will  look  like  the  cooling  curve  of  axpure  substance,  and 
show  a  horizontal  arrest  at  that  temperature.  Solutions  which 
contain  more  than  23.5  per  cent  of  salt  have  cooling  curves  exactly 
similar  to  solutions  poor  in  salt;  that  is,  they  possess  an  arrest 
(or,  more  correctly,  a  change  in  direction)  at  <ome  temperature 
higher  than  —22°  C.  as  well  as  a  horizontal  arrest  at  that 
temperature.  For  instance,  a  concentration  of  27  per  cent  salt 
and  73  per  cent  water  begins  to  deposit  crystals  of  pure  salt 
at  its  first  arrest.  The  remaining  mother  liquor  consequently 
becomes  poorer  in  salt  until  the  analysis  23.5  per  cent  salt, 


LEAD-ANTIMONY  ALLOYS  73 

76.5  per  cent  water  is  reached,  which  as  before  must  solidify 
at  -22°  C. 

Such  a  mother  liquor,  which  always  has  the  same  composi- 
tion in  the  same  alloy  system,  possesses  a  constant  freezing- 
point,  and  remains  liquid  longest  of  the  whole  series  of  solu- 
tions, is  called  the  "  eu  tec  tic  " — literally,  "  low-melting." 

The  property  of  the  eutectic  in  possessing  a  constant  melting- 
point,  and  therefore  a  constant  composition,  led  formerly  to  the 
belief  that  it  was  a  chemical  compound.  From  more  exact 
investigations,  however,  it  was  shown  that  the  components 
are  not  in  any  simple  molecular  ratio.  Further,  the  microscope 
established  the  fact  that  the  eutectic  is  not  a  homogeneous 
substance,  but  a  mechanical  mixture  of  an  innumerable  number 
of  minute  crystals  of  two  separate  substances.  In  the  water- 
salt  system,  the  liquid  eutectic  may  be  regarded  simultaneously 
as  a  concentrated  solution  of  water  in  salt,  and  a  concentrated 
solution  of  salt  in  water.  Further  cooling  cannot  enrich  either 
solution,  and  therefore  it  must  solidify  at  a  constant  tempera- 
ture. The  two  materials  are  insoluble  in  each  other  in  the  solid 
state;  consequently  they  separate  out  simultaneously,  side 
by  side. 

In  order  to  systematize  our  information  on  this  alloy  system, 
let  the  temperature  of  the  melting-points,  or  of  any  other  arrest 
on  the  cooling  curves,  be  plotted  vertically  to  scale  as  ordinates, 
and  let  the  abscissae  represent  the  composition  of  the  corre- 
sponding mixtures — in  this  instance,  the  percentage  of  salt  con- 
tained in  this  particular  alloy.  Evidently,  the  Y-axis  represents 
all  conditions  for  pure  water,  for 

x  =  o,  where  #  =  per  cent  salt  in  the  solution. 

The  diagram  can  continue  to  the  right  no  further  than  100  units, 
representing  pure  salt.  A  vertical  line  erected  half-way  across 
will  show  conditions  as  they  exist  at  any  temperature  for  an 
alloy  containing  50  per  cent  water,  50  per  cent  salt,  and  so  on. 

In  Fig.  9,  the  arrests  and  changes  in  direction  noted  in  the 
cooling  curves  discussed  above  have  thus  been*  plotted,  and 


74 


EXPERIMENTAL  GROUP  II 


smooth  connecting  curves  drawn.  Notations  have  been  made  on 
the  lines  and  areas  of  this  equilibrium  diagram  which  are  self- 
evident  in  the  light  of  the  previous  discussion,  and  a  brief 
consideration  will  indicate  how  the  diagram  shows  the  physical 
condition  of  every  possible  solution  of  salt  and  water  at  any 


+30° 

THE  WATER-SALT 
EQUILIBRIUM  DIAGRAM 

C.  C.   (Z/riusrYLs 

+20° 

/ 

J 

+10° 

i 

LIQ 

UID 

j 

9t 

jrc 



t^ywi 

^cv, 

i 

-10° 

- 

^    . 

«? 

7 

ICE 
MO" 

CRY' 
HER 

JTALS  IN 
LIQUOR 

X 

*0 

« 

9 

SALT  CRYSTALS  IN 
MOTHER  LIQUOR 

-20° 

| 

\ 

a 

0 

2 

Motht 

r     Liq 

uor    rjeaches 

Eute 

ctic    ( 

ompo 

-.ition 

^2. 

and    Solidifi 

es 

| 

a 

-30° 

PRII 

rtARY 

ICE 

IN  E 

JTEC 

TIC 

3 

PRI 

MAR^ 

'  SAL 

T  IN 

EUT 

ECTK 

i 

"6*. 

S 

i 

I 

-s 

^ 

^Wei 

ghtP 
intt 

;r  cer 

eMb 

tof\ 
ture 

^ater 

s 

o 

•re 

I 

i 

•^, 
& 

r-Wei 

'  in  tl 

r  cen't  of  J 
e  Mixture 

ad 

FIG.  9. — The  Water-Salt  Equilibrium  Diagram. 

conceivable  temperature,  the  pressure  remaining  constant  at  one 
atmosphere. 

This  simple  case  is  given  at  some  length  as  an  example 
of  equilibrium  conditions  and  diagrams  because,  as  mentioned 
at  the  outset,  it  is  typical  of  most  of  the  important  metallic 
alloys,  and  because  it  is  made  from  the  freezing  mixtures  so 
common  in  the  household  ice-cream  freezer.  The  underlined 
V  (V)  is  an  element  recognized  in  even  the  most  complicated 
equilibrium  diagrams. 


LEAD-ANTIMONY  ALLOYS  75 

Special  Apparatus.  The  special  apparatus  needed  is  as 
follows: 

One  electrical  meter. 

The  following  will  be  issued  to  alternate  squads,  who  will 
interchange  them  as  needed: 

Four  oooo  graphite  crucibles. 

One  5oo-gm.  button  of  each  of  the  following: 

Sb    6    per  cent  Pb  94     per  cent 

Sb  12.5  Pb  87.5 

Sb  25  Pb  75 

Sb  50  Pb  50 

Supplies.     The  supplies  needed  are  as  follows: 

Ice. 
Charcoal. 

Laboratory  Equipment.  The  laboratory  equipment  needed  is 
as  follows: 

Bucking-board  and  muller. 

Procedure,  a.  With  a  sharp  knife  cut  a  number  in  the  side 
of  the  crucibles  corresponding  to  the  percentage  of  antimony 
contained  in  the  alloys. 

6.  Melt  the  alloy  slowly  in  a  pot  furnace  under  a  heavy 
cover  of  fine  charcoal.  Avoid  raising  the  temperature  much 
above  the  temperatures  given  below,  or  breathing  the  fumes 
rising  from  the  pot. 

6  per  cent  antimony  alloy,  350°  C 
12.5  per  cent  antimony  alloy,  350 
25  per  cent  antimony  alloy,  450 
50  per  cent  antimony  alloy,  600 

c.  Place  the  cover  on  the  pot  furnace.  Slowly  heat  the 
thermo-couple  junction  to  about  the  temperature  of  the  melt 
in  the  flames  issuing  thru  the  opening  in  the  furnace  cover. 


76  EXPERIMENTAL  GROUP  II 

Lower  the  hot  junction  into  the  center  of  the  melt  and  hold  it 
there  with  a  condenser  clamp  and  ring  stand. 

d.  Immerse  the  cold  junction  in  the  ice  bath,  and  connect 
the  leads  to  the  meter.     Remove  the  blast  lamp  as  soon  as  the 
hot  junction  registers  the  temperature  of  the  bath. 

e.  Read  the  dial  on  the  meter  to  one-tenth  unit  at  fifteen- 
second  intervals ;  record  and  plot  the  observations  until  the  tem- 
perature has  fallen  to  200°  C.     After  each  reading,  the  meter 
may  be  tapped  gently  with  the  fingers  to  prevent  the  needle  from 
lagging.     During  the  early  part  of  the  cooling,  move  the  thermo- 
couple back  and  forth  in  the  melt  horizontally,  using  it  as  a 
stirring  rod  to  prevent  segregation  of  the  alloy.     Be  careful 
not  to  lift  the  welded  junction  above  the  center  of  the  melt. 
When  the  alloy  becomes  mushy,  fix  the  junction  at  the  center  of 
the  melt  with  the  clamp. 

/.  The  time-temperature  curve  constructed  as  above  is  not 
well  adapted  to  show  small  evolutions  of  heat  in  an  alloy. 
Construct  an  "  inverse  rate  curve  "  for  the  alloy  (which  will 
magnify  the  changes  in  direction  of  the  cooling  curve)  as  follows : 
Remelt  the  alloy,  and  cool  with  constant  stirring  as  in  proce- 
dure e.  Post  one  of  the  squad  members  near  the  meter  with  a 
watch  and  have  him  read  and  note  the  time  to  a  second  when 
the  meter  needle  reaches  each  half-unit.  When  the  cooling  is 
finished,  subtract  each  time  reading  from  its  immediate  pre- 
decessor; the  difference  will  give  the  time  required  to  cool  the 
alloy  thru  one-half  unit,  or  the  rate  of  cooling  at  that  tem- 
perature. Plot  these  rates  against  meter  readings,  and  connect 
with  a  smooth  curve. 

g.  Present  both  curves  to  a  laboratory  officer  for  inspection 
and  approval. 

h.  When  a  satisfactory  check  has  been  secured,  melt  the 
couple  free  from  the  bath,  and  allow  the  metal  to  cool  in  the  cru- 
cible. Melt  away  any  alloy  adhering  to  the  insulation  by 
holding  it  in  the  flame  of  the  blast  lamp.  Examine  the  insula- 
tion carefully  for  breaks,  and  repair  it  with  retort  cement  if 
necessary. 


LEAD-ANTIMONY  ALLOYS  77 

i.  Repeat  the  above  procedure  c  to  i  inclusive  for  each  of 
the  four  alloys. 

j.  At  the  end  of  the  day,  cover  the  couple  with  a  fresh 
layer  of  insulating  cement  and  lay  away  to  dry  over  night. 

Queries,  a.  Make  an  equilibrium  diagram  of  the  lead- 
antimony  system  with  India  ink  on  standard  cross-section  paper, 
using  the  exact  form  of  Fig.  9.  The  data  for  this  diagram  has 
been  derived  in  Experiments  Nos.  8,  9  and  10.  Plot  the  Shore 
scleroscope  hardness  (Experiment  No.  13)  for  each  alloy  and  the 
pure  metals  on  this  diagram,  and  connect  the  plots  with  a  red 
line. 

b.  Explain  the  reasons  for  the  action  which  occurs  when 
one   strews  salt  on   an  icy  sidewalk.      Would   this  expedient 
remove  ice  at  any  temperature? 

c.  Give   some  practical  applications  of  the  lead-antimony 
alloys. 

d.  Show  the  derivation  of  the  following  from  the  equilib- 
rium diagram:     ist,  What  is  the  state  of  a  40  per  cent  lead, 
60  per  cent  antimony   alloy  at   450°    C.?     2d,  What   is   the 
composition  of  the  mother  liquor  when  this  alloy  has  cooled  to 
325°   C.?     3d,  How  much  antimony,  per  gram  of  the  alloy, 
has  crystallized  out  when  it  has  cooled  to  275°  C.?    4th,  How 
much  eutectic,  per  gram,  will  appear  when  this  alloy  is  entirely 
solidified? 

e.  Suppose  the  eutectic  to  be  a  chemical  compound,  figure 
a  formula  for  it. 


EXPERIMENTAL  GROUP  III 
FOREWORD  TO  THE  STUDENT 

Group  III  contains  a  number  of  experiments  of  rather  general 
application.  They  have  been  separated  from  Group  I,  since 
it  is  important  that  the  student  learn  the  elements  of  pyrometry 
as  soon  as  possible.  Then,  too,  some  of  the  experiments  will 
probably  not  be  performed  by  all  students.  As  an  instance, 
Experiment  No.  14  on  electric  furnaces  may  be  confined  to 
Electrical  Engineering  students.  Other  experiments  will  form 
the  basis  of  extensive  advanced  work  for  metallurgical  special- 
ists, such  as  Experiments  Nos.  n  and  12,  on  metallography  and 
photomicrography. 

Experiment  No.  13,  covering  hardness,  is  presented  in  this 
place  rather  than  in  a  course  on  the  strength  of  materials,  chiefly 
because  it  is  of  most  value  in  the  testing  of  heat-treated  tools 
and  machine  parts. 

Experiment  No.  15  on  radiation  and  optical  pyrometry  is 
separated  from  Group  II  more  because  of  the  rather  special  and 
complex  underlying  theory,  than  of  the  difficulty  of  their  manipu- 
lation. At  some  time  in  the  course,  each  student  should  have 
an  opportunity  to  handle  these  remarkable  instruments  of  pre- 
cision. 


78 


EXPERIMENT  NO.  11 
METALLOGRAPHY 

Object.  The  object  of  this  experiment  is  to  examine  the 
internal  structure  ("  constitution  ")  of  metallic  substances. 

General  Explanation.  The  use  of  the  microscope  to  examine 
the  constitution  of  metals  is  a  long  step  in  advance  of  the  ancient 
practice  of  breaking  a  bar  and  looking  at  the  fracture.  It 
offers  a  means  whereby  the  apparent  size  of  the  grains  may  be 
magnified  to  any  desired  degree  up  to  the  limits  of  microscopic 
enlargement,  altho  a  moderate  magnification  will  usually 
suffice  to  bring  out  the  structure  excellently  well.  For  the  great 
bulk  of  routine  work,  therefore,  a  low-priced  lens  outfit  consist- 
ing of  two  objectives  and  two  eyepieces  (giving  magnification 
of  50  diameters,  75  diameters,  100  diameters,  and  150  diam- 
eters) is  all  that  is  required. 

Excellent  microscopes  have  been  built  especially  for  metal- 
lographic  work,  but  an  ordinary  biological  microscope  can  be 
easily  adapted  to  the  examination  of  metals.  Metallographic 
work  requires  an  unique  method  of  illumination,  as  it  deals  with 
opaque  objects,  and  the  substage  illuminator  used  by  the  biolo- 
gist in  examining  transparent  sections  by  transmitted  light  is 
consequently  of  no  service.  The  attachment  takes  the  form 
of  a  "  vertical  illuminator  "  or  "  plane-glass  reflector  "  screwed 
into  the  draw  tube  of  the  microscope  between  the  eyepiece  and 
the  objective.  This  reflector  consists  merely  of  a  prism  or 
plate  of  glass  mounted  on  a  horizontal  pivot,  and  capable  of 
adjustment  in  such  a  way  as  to  reflect  a  beam  of  light  from  an 
outside  source  down  thru  the  lenses  of  the  objective  upon  the 
specimen  under  examination,  from  which  the  light  is  then  re- 
flected directly  back  thru  the  optical  system  to  the  eye. 

79 


80  EXPERIMENTAL  GROUP  III 

For  this  reason,  the  surface  of  the  _specimen  must  be  prepared 
so  as  to  have  a  reflecting  surface.  Soft  metals  and  alloys  should 
be  first  smoothed  off  with  a  fine- toothed  file,  well  oiled;  only 
hard  metals  should  be  placed  on  the  emery  wheel.  The  samples 
are  then  ground  on  canvas-covered  disks  charged  with  abrasive 
powders  of  successive  degrees  of  fineness,  or  on  finest  emery 
paper,  ranging  from  o  to  oooo,  laid  over  a  plate  glass.  Final 
polishing  is  done  on  a  wet  broadcloth-covered  disk  using  jeweler's 
rouge  as  an  abrasive. 

The  method  of  mounting  a  specimen  so  that  the  polished 
surface  is  parallel  to  the  stage  and  therefore  perpendicular  to 
the  optical  axis  of  the  microscope  is  an  important  and  often- 
times a  troublesome  detail.  The  method  shown  in  procedure  / 
is  simple  and  highly  satisfactory  for  moderate-sized  specimens. 

The  methods  outlined  above  will  give  a  surface  free  from 
scratches  and  brightly  reflecting,  but  will  not  generally  bring 
out  the  internal  structure.  Where  the  alloy  consists  of  hard 
and  soft  particles,  the  final  polishing  on  a  soft  cloth  disk  will 
often  differentiate  between  the  constituents  by  relief — the  harder 
constituent  withstanding  erosion,  while  the  softer  is  depressed. 
Ordinarily,  however,  it  is  necessary  to  etch  the  surface  with 
acids  which  corrode  one  constituent  more  rapidly  than  the  other. 
Obviously,  uncorroded  parts  of  the  surface  still  brightly  reflect 
light  and  will  appear  bright  or  white  under  the  microscope; 
other  parts  which  have  been  corroded  will  appear  gray  to 
black,  depending  upon  the  amount  of  incident  light  which  is 
dispersed  or  absorbed.  Or,  again,  one  may  produce  differences 
due  to  natural  colorations  in  the  alloy,  or  due  to  selective  stain- 
ing by  the  corrosive  medium. 

Further  and  detailed  descriptions  of  the  metallurgical  micro- 
scope and  methods  for  preparation  and  examination  of  sections 
can  be  found  in  "  The  Metallography  and  Heat  Treatment  of 
Iron  and  Steel  "  by  Albert  Sauveur,  Chapters  I  to  III  inclu- 
sive. 

Special  Apparatus.  The  special  apparatus  needed  is  as  fol- 
lows: 


METALLOGRAPHY  81 

One  o.i-gm.  trip  balance  and  weights. 
One  piece  of  plate  glass,  12  in.  square. 
One  towel. 

Supplies.     The  supplies  needed  are  as  follows: 

One  5-gm.  crucible. 

Twenty  grams  pure  antimony. 

Six-inch  square  piece  of  emery  papers,  o,  oo,  ooo,  ooo. 

One  piece  of  broadcloth,  14  in.  square. 

Five  large  manila  envelopes. 

Metallurgical  Laboratory  Equipment.     The  equipment  needed 
in  the  metallurgical  laboratory  is  as  follows: 

Lead. 

Piece  of  i-in.  pine  board. 

Oil  can. 

Erlenmeyer  flask  with  polishing  rouge. 

Metallography  Room  Apparatus.     The  apparatus  needed  in 
the  metallography  room  is  as  follows: 

Bunsen  burner. 

Crucible  tongs. 

Concentrated  nitric  acid. 

Porcelain  crucible. 

Microscopic  sets,  each  containing 

Brass  mounting  cup, 

Can  of  BB  lead  shot, 

Cover  glass, 

Candle  lamp  and  condensing  lens,  complete, 

Metallographic  microscope;  with 

Plane  glass  reflector, 
Oculars,  5X,  loX, 
Objectives,  8mm.,  16  mm. 

Procedure,     a.  Melt  the  antimony  in  a  new  5-gm.  crucible. 
Stir  with  a  splinter  of  wood,  and  cast  into  a  clean,  warm  button 


82  EXPERIMENTAL  GROUP  III 

mold.     Saw  a  cube  of  metal  from  this  button,  about  f  in.  on  a 
side. 

b.  Make  up  the  trimmings  from  this  antimony  button  into 
an  alloy  containing  3  per  cent  Pb,  97  per  cent  Sb,  by  melting 
the  more  refractory  metal  and  then  carefully  adding  the  more 
fusible  substance.     Stir  well  with  a  splinter  of  wood,  and  cast 
quickly  into  a  clean,  warm  button  mold.     CAUTION:     Guard 
against  spitting  or  explosions  when  adding  cold  metal  to  a 
melt.     Do  not  heat  the  metal  much  above  the  melting-point. 

c.  Oil  a  fine-toothed  file  and  smooth  one  surface  of  each 
sample  flat. 

d.  Grind  off  the  file  marks  by  rubbing  lightly  back  and  forth 
on  a  piece  of  o  emery  paper  laid  over  a  piece  of  plate  glass. 
Hold  and  move  the  sample  in  such  a  way  that  the  motion  will  be 
at  right  angles  to  the  scratches  left  by  the  preceding  operation. 
Polish  until  these  scratches  are  eliminated. . 

e.  Continue  the  process  from  finer  to  finer  papers,  lastly 
polishing  on  a  piece  of  wet  broadcloth  stretched  over  the  plate 
and  moistened  with  rouge.     Wash  the  specimen  and  hands  before 
transferring  to  a  finer  emery,  being  very  careful  to  prevent  coarse 
grit  from  lodging  on  a  finer  paper,  for  should  this  occur,  deep 
scratches  will  be  cut  into  the  metal  which  can  not  be  readily 
polished  off.     Preserve  the  abrasive  fabrics  by  placing  them  into 
separate  envelopes. 

/.  Mount  the  specimen  in  a  small  brass  cup  which  has  the 
top  edge  and  bottom  surface  milled  precisely  parallel.  Partly 
fill  the  cup  with  small  lead  shot,  lay  in  the  specimen  with  polished 
face  uppermost,  and  press  it  down  into  the  shot  with  a  cover 
glass  until  the  glass  rests  upon  the  top  of  the  cup. 

g.  Set  up  the  microscope  as  follows:  Screw  the  plane  glass 
reflector  A  (Fig.  10)  into  the  top  of  the  objective  B  and  then 
screw  the  combination  into  the  bottom  of  the  draw  tube  C. 
Place  an  eyepiece  D  into  the  top  of  the  draw  tube,  selecting 
such  a  combination  of  ocular  and  objective  as  will  give  a  magnifi- 
cation of  about  50  diameters.  Place  the  brass  mounting  cup 
on  the  stage  E,  bringing  the  specimen  into  approximate  focus  by 


METALLOGRAPHY  83 

thumbscrew  F.  Then  adjust  an  incandescent  "  candle-lamp  " 
at  the  level  of  the  opening  in  the  plane  glass  reflector,  and  at  the 
focus  of  an  intervening  condensing  lens  which  will  project  a 
parallel  beam  of  light  into  the  reflector.  Turn  the  reflecting 
glass  by  means  of  thumb  nut  G  until  a  bright  spot  of  light 
appears  on  the  sample.  Then  place  the  eye  at  the  ocular  D  and 
focus  exactly  by  the  stage  pinon  F  and  the  micrometer  screw  H. 


FIG.  10. — Metallographic  Microscope. 

h.  Examine  both  specimens  in  this  manner,  noting  any 
difference  in  their  appearance. 

i.  Etch  the  polished  specimen  of  pure  antimony  as  follows: 
Place  5  cu.cm.  of  concentrated  HNOs  in  a  small  porcelain 
crucible,  and  heat  over  a  Bunsen  flame  placed  in  a  hood.  Drop 
the  specimen  carefully  into  the  hot  acid  so  that  the  polished  face 
is  exposed  to  its  attack  for  five  seconds.  Then  stop  the  action 
and  wash  off  the  specimen  by  holding  the  crucible  under  running 


84  EXPERIMENTAL  GROUP  III 

water.  The  surface  is  now  covered  by  a  white  crust  of  insoluble 
antimonic  acid,  which  can  be  removed  by  a  very  light  polishing 
on  the  rouge-covered  broadcloth. 

j.  Examine  the  whole  surface  carefully  under  the  micro- 
scope, observing  whether  the  boundaries  of  the  crystalline  grains 
are  well  defined.  If  not,  repeat  procedure  i  until  the  sample  is 
regarded  as  satisfactory  by  the  instructor. 

k.  Repeat  procedure  i  and  j  with  the  lead-antimony  alloy. 

/.  Draw  the  appearance  of  each  specimen  on  a  standard 
sheet  of  blank  paper  with  a  hard,  sharp  pencil.  Note  below 


Ferrite 


toff,  Dappled, 

Three  different 

hades. 


FIG.  ii. — Free  Hand  Micrograph  of  Wrought  Iron. 

each  sketch  the  material,  magnification,  and  etching.  Name  the 
various  structural  constituents  occurring  in  the  field  and  indicate 
their  position  by  arrows.  These  sketches  should  be  carefully 
done  by  each  student  individually,  somewhat  like  Fig.  n,  and 
they  must  be  accepted  by  the  instructor  before  the  student  leaves 
the  laboratory. 

Queries,  a.  Why  do  the  crystalline  grains  of  pure  antimony 
interlock  with  each  other,  developing  no  clearly  defined  facets? 

b.  What  is  the  difference  between  a  crystalline  body  and  an 
amorphous  body?  How  do  you  know  that  these  metallic  grains 
have  a  true  crystalline  structure? 


METALLOGRAPHY  85 

c.  The  minute  black  spots  appearing  under  the  microscope 
in  the  lead-antimony  alloy  may  be  one  of  these  things: 

ist,  Pure  lead. 

2d,    A  lead-antimony  alloy. 

3d,    A  cavity. 

4th,  An  impurity. 

Which  of  these  things  is  it,  and  why? 

d.  One  and  three- tenths  grams  of  lead  were  added   to   a 
crucible    containing    102.6    gm.    antimony.     After    casting,    it 
was  analyzed  and  found  to  contain  0.93   per  cent  lead.     Ex- 
plain  the  reason  for  the  metal  losses  and  indicate  methods   to 
prevent  it. 

e.  What  influence  will  the  rate  of  cooling  have  upon  the 
size  of  the  crystalline  grains? 

/.  What  can  you  say  from  the  results  of  this  experiment 
about  the  mutual  solubility  of  lead  and  antimony? 


EXPERIMENT  NO.  12 
PHOTOMICROGRAPHY 

Object.  The  object  of  this  experiment  is  to  photograph  the 
constitution  of  a  metallic  substance. 

General  Explanation.  Experiment  No.  1 1  mentioned  the  ad- 
vantages of  microscopic  examination  of  metallic  structure.  It  is 
just  as  desirable  to  make  a  permanent  record  of  the  appearances 
thus  revealed.  The  advantages  of  these  records  are  that  they 
may  be  indefinitely  multiplied,  minutely  studied  and  compared 
at  leisure  and  at  distant  times  and  places.  As  in  the  case  of 
astronomy,  the  photographic  plate  may  even  reveal  minute 
details  otherwise  unseen. 

Of  course,  the  method  of  photographic  manipulation  will 
vary  with  the  kind  of  apparatus,  which  in  turn  depends  upon  the 
ideas  used  by  the  makers.  In  general,  however,  the  procedure 
is  as  follows:  The  specimen  is  polished,  etched,  mounted,  and 
examined  as  directed  in  Experiment  No.  n.  When  an  area 
deemed  proper  to  photograph  is  found,  the  ocular  is  replaced  by  a 
suitable  projection  lens,  and  a  light-tight  connection  made  to  a 
camera  box.  This  box  is  supported  firmly  in  such  a  way  that  the 
back  is  at  right  angles  to  the  optical  axis  of  the  microscope. 
By  lifting  or  lowering  the  stage  the  image  is  then  focused  on 
the  ground  glass  plate  which  forms  the  back  of  the  camera 
box.  A  loaded  plate  holder  now  replaces  the  ground  glass,  and 
the  plate  is  exposed  the  proper  length  of  time,  developed,  and 
printed  by  the  ordinary  methods  of  photographic  manipulation. 

Personal  experience  alone  can  perfect  the  minute  details 
necessary  to  the  production  of  uniformly  good  photographs. 
For  this  reason,  only  general  instructions  can  be  given,  which 
may  be  modified  to  meet  the  conditions  of  individual  cases. 

86 


PHOTOMICROGRAPHY  87 

Orthochromatic,  slow;  plates  (or  "  process  "  plates)  are  best 
for  two  reasons:  first,  a  slow  plate  will  reproduce  much  more 
minute  details  than  a  fast  plate;  and  second,  extreme  care 
is  necessary  to  prevent  "  fogging  "  of  fast  plates  during  loading, 
exposure  and  development.  A  ray  filter  of  colored  glass  inserted 
between  the  lamp  and  plane  glass  reflector  will  furnish  mono- 
chromatic light,  which  will  give  a  negative  with  great  contrast. 
Intense  light  is  needed  for  high  magnifications,  which  also,  in 
general,  require  a  longer  exposure  than  low  powers. 

The  time  of  exposure  is  governed  by  the  nature  of  the  source 
of  light,  the  speed  of  the  plate,  the  magnification,  and  the  color 
and  contrast  in  the  sample.  It  therefore  varies  so  widely  that  it 
is  impossible  to  give  any  useful  rule  for  its  computation.  The 
best  way  to  arrive  at  the  correct  time  for  given  conditions  is  to 
expose  a  trial  plate  en  echelon  as  follows:  Draw  out  the  slide 
shutter  from  in  front  of  the  plate,  and  expose  for  a  certain  meas- 
ured number  of  seconds,  which  is  somewhat  less  than  the  expected 
time  necessary.  Push  in  the  shutter  to  cover  about  one-fifth 
of  the  plate,  cutting  off  the  light  as  the  slide  is  pushed  in.  Then 
expose  for  another  measured  interval  of  time.  Continue  the 
exposure  strip  by  strip  in  this  fashion,  thus  giving  to  the  middle 
strip  that  time  estimated  to  be  correct.  When  the  plate  is  de- 
veloped, the  intensity  of  the  negative  will  vary  strip-wise, 
and  it  will  at  once  furnish  an  index  of  the  best  exposure. 
The  under-exposed  strips  will  be  thin  and  transparent,  those 
exposed  correctly  will  be  dense  and  rich  in  contrast,  while  the 
over-exposed  strips  will  present  a  fogged,  appearance. 

The  proper  development  of  the  plate  furnishes  a  permanent 
negative  from  which  an  indefinite  number  of  prints  can  be  made. 
Contact  printing  papers  can  be  purchased  in  a  great  variety  of 
grades  suitable  for  a  wide  range  of  negatives  from  strong  to 
weak.  A  proper  selection  will  furnish  prints  which  are  brilliant 
and  vigorous  in  their  gradations  from  black  to  white.  These 
papers  may  have  a  rough  or  smooth  matte  finish,  or  a  glossy 
surface,  the  brilliancy  of  which  may  be  heightened  by  glazing. 
Directions  for  exposure,  development  and  fixing  vary  with 


88  EXPERIMENTAL   GROUP  III 

the  kind  of  paper  in  use;  the  printed  directions  accompanying 
the  supplies  may  be  followed.  In  case  the  commercial  tube 
developers  do  not  give  the  desired  results  (as  is  oftentimes  the 
case)  the  following  developer  recommended  by  Leitz  may  be 
advantageously  employed : 

Water,  i  liter 

Metol,  6  gm. 

Sodium  sulfite,  50  gm. 

Hydroquinone,  2  gm. 

Potash,  20  gm. 

Potassium  bromide,  i  gm. 

Dissolve  in  the  exact  order  in  which  they  are  named,  and  dilute 
with  three  parts  of  water.  No  more  of  this  developer  should 
be  made  than  is  to  be  used  at  one  time. 

The  following  tips  may  be  of  service:  Weak  negatives  are 
due  to  under-exposure  if  the  negatives  are  thin  with  clear 
shadows,  but  to  under-development  if  the  detail  is  obscured  by 
shadows.  Fogged  negatives  may  be  due  to  an  unsafe  dark 
room,  a  leaky  camera  box  or  plate  holder,  prolonged  over- 
exposure  or  over-development,  or  warm  developer.  Yellow 
stains  on  negative  are  due  to  insufficient  rinsing  before  fixing, 
or  to  stale  solutions.  Blisters  on  the  gelatine  are  due  to  warm 
solutions;  use  cracked  ice  in  solutions  and  harden  with  an 
alum  bath.  Halation  is  caused  by  light  passing  thru  the 
emulsion  and  being  reflected  from  the  clear  side.  Deposits 
on  negatives  are  usually  due  to  cloudy  solutions  or  dirty  wash 
water,  and  may  be  removed  by  rubbing  the  dry  negative  with 
cotton  moistened  with  alcohol. 

Correctly  exposed  prints  will  develop  to  a  proper  point  and 
then  stop.  Allowing  the  print  to  remain  in  the  solution  will 
cause  yellow  stains.  Flat  muddy  prints  are  usually  due  to 
over  exposure;  use  a  harder  grade  of  paper  to  fit  the  negative. 
Spots  on  prints  may  be  due  to  air  bubbles  on  the  surface  of  the 
print  during  development,  or  to  abrasion  of  the  sensitive  coating 


PHOTOMICROGRAPHY  89 

before  development.     Most  of  the  other  faults  of  prints  are  due 
to  the  same  causes  as  noted  above  for  plates. 

Special  Apparatus.     The  special-apparatus  needed  is  as  fol- 
lows: 

Scissors. 

Fine  file. 

Polishing  machine,  including 

Motor, 

Three  canvas-covered  disks, 
One  broadcloth-covered  disk, 
Four  bell  jars, 

Four    corked    Erlenmeyer    flasks    with    suitable 
abrasives. 

Microscopic  set,   including 

Brass  mounting  cup, 

Can  of  BB  lead  shot, 

Cover  glass, 

Candle  lamp  and  condensing  lens,  complete, 

Metallographic  microscope,  with 

Plane  glass  reflector. 
Oculars,  5X,  loX, 
Objectives,  8  mm.,  16  mm. 

Photographic  set,  including 

Three  plate  holders, 

Focusing  cloth, 

Camera  box, 

Light  filter, 

Tray  for  developer, 

Tray  for  rinsing  solution, 

Fixing  tank, ' 

Washing  tank, 

Soft  sponge, 

Printing  frame, 

Plate  rack. 


90  EXPERIMENTAL  GROUP  III 

Supplies.     The  supplies  needed  are  as  follows: 

Three-eighth  inch  cube  of  50  per  cent  Pb,  50  per  cent  Sb 

alloy. 
Ice. 

Piece  of  cotton. 
Tube  of  print  developer. 
Box  of  twelve  process  plates. 

Envelope  of  12  hard  photographic  printing  papers. 
Envelope  of  12  pieces  Kodak  dry  mounting  tissue. 

Metallography  Room  Equipment.     The  equipment  needed  in 
the  metallography  room  is  as  follows: 

Warm  air  blast. 

Electric  flat-iron. 

Graduate. 

Stand  of  brass  pins. 

Oil  can  with  cylinder  oil. 

Vise. 

Analytical  balance  and  weights. 

Dark  room  equipped  with  ruby  light,  work  table,  printing 

box  and  sink. 
Developing  solution  No.  i : 

Water,  i  liter 

Dry  Na2SO?,  50  gm. 

Hydroquinone,        15.5  gm. 

Developing  solution  No.  2 : 

Water,  i  liter 

NaOH,  ii  gm. 

KBr,  5.5  gm. 

Fixing  solution  of  commercial  acid  fixing  powder. 
Saturated  solution  of  alum. 


PHOTOMICROGRAPHY  91 

Clearing  solution: 

Water,  i  liter 

Citric  acid,  4  gm. 

Alum,  40  gm. 

Procedure,     a.  Polish  one  surface  of  the  alloy  according 
to  Experiment  No.  n,  procedure  c  to  e  inclusive. 

b.  Open  the  box  of  plates  in  the  dark  room  only  long  enough 
to  remove  one  plate.     Distinguish  between  the  sensitive  and  bare 
side  of  the  plate  by  touch,  or  by  observing  the  reflection  of  the 
ruby  lamp,  using  the  plate  as  a  mirror.     The  bare  side  will 
reflect  sharply,  while  the  coated  side  will  show  as  thru  a  fog. 
Number  the  plates  serially,  and  also  write  your  initials  on  one 
corner  of  the  emulsion-coated  side  with  a  sharp  lead  pencil. 
Load  the  plate  holder  with  the  sensitive  side  next  to  the  slide 
shutter,  closing  the  front  of  the  frame. 

c.  Mount  the  specimen  under  the  microscope  (procedure  / 
and  g,  Experiment  No.  n),  and  select  some  region  where  the 
primary  crystals  are  sharply  formed,  and  the  structure  of  the 
eutectic  cement  is  clearly  discernible.     Replace  the  ocular  by 
the  projection  lens,  and  fix  the  camera  box  rigidly  above  the 
microscope,  making  a  light  proof  connection  to  the  draw  tube. 
Focus  the  image  on  the  ground  glass  by  means  of  the  stage 
pinion  and  micrometer  screw,  excluding  outside  light  with  a  focus- 
ing cloth.     Adjust  the  candle  lamp  and  plane  glass  reflector  so 
that  the  image  is  evenly  illuminated  and  free  from  color  fringes. 
Exhibit  the  image  to  an  instructor. 

d.  Close  the  shutter,  if  the  camera  box  is  supplied  with  one,  or 
put  out  the  candle  lamp.     Replace  the  ground  gass  with  the  plate 
holder,  and  pull  out  the  slide  shutter  in  front  of  the  plate.    All 
is  now  ready  for  the  exposure,  which  is  made  by  simply  opening 
the  shutter  or  burning  the  candle  lamp  for  the  required  time. 

e.  Determine  the  time  necessary  by  exposing  the  first  plate 
en  echelon,   as   described    in   the    general   explanation   above. 
Close  the  slide  shutter  completely,  and  remove  the  plate  holder 
to  the  dark  room. 


92  EXPERIMENTAL  GROUP  III 

/.  Develop  the  plate  as  follows:  In  a  tray  place  50  cu.cxn. 
each  of  developing  solutions  i  and  2,  with  a  few  small  pieces 
of  ice.  Take  out  the  exposed  plate,  and  immerse  it  in  the  solu- 
tion, grasping  it  by  the  edges.  Rub  the  entire  surface  with  a 
piece  of  wet  cotton  to  free  it  from  air  bubbles  and  dust  particles. 
The  plate  should  be  rocked  back  and  forth  continuously  under  the 
solution  for  a  sufficient  time  (usually  in  the  neighborhood  of  five 
minutes).  The  image  of  the  round  exposed  field  should  appear 
in  less  than  a  minute;  somewhat  later  will  appear  the  sharp 
outlines  of  the  crystals.  Continue  the  development  until  the 
whole  exposure  becomes  very  black  and  dense,  and  the  sharp 
outlines  are  once  more  obscured. 

g.  When  the  plate  is  developed,  wash  it  thoroly  in  cold 
water  and  drop  it  gently  in  a  hard  rubber  tank  filled  with  the 
iced  fixing  solution.  Allow  the  plate  to  remain  here  for  at  least 
ten  minutes,  or  until  it  looks  perfectly  clear — all  milkiness 
should  have  vanished  from  the  unexposed  corners  of  the  plate. 

h.  Wash  the  plate  in  the  washing  tank  in  a  continuous 
stream  of  cold  water  for  half  an  hour.  Then  carefully  rub  the 
plate  with  a  soft  sponge,  and  immerse  it  in  a  tank  of  saturated 
alum  solution  for  five  minutes  to  harden  the  gelatine.  Remove, 
wash  briskly  in  running  water,  shake  off  excess,  and  dry  in  front 
of  a  warm  air  blast. 

i.  Discuss  the  results  of  the  trial  exposure  with  a  labora- 
tory officer,  and  decide  upon  the  correct  time.  Reload  the  plate 
holder  as  in  6,  refocus  the  image  on  the  ground  glass,  expose  the 
plate  the  required  time,  and  develop  the  plate  as  above,  procedure 
/  to  h  inclusive.  Exhibit  the  results  to  an  instructor. 

j.  Make  two  prints  from  this  negative  as  follows:  Remove 
one  piece  of  the  photographic  print  paper  from  the  envelope 
in  the  dark  room.  Place  the  prepared  side  of  the  paper  against 
the  gelatine  on  the  negative,  and  put  the  combination  into  the 
printing  frame.  Expose  in  the  printing  box  for  a  time  as 
directed  by  the  instructions  or  as  determined  by  trial.  Replace 
the  developing  solution  for  developing  plates  with  another  solu- 
tion made  with  the  tube  of  print  developer,  and  develop  in  ruby 


PHOTOMICROGRAPHY  93 

light  after  procedure  /,  with  the  exception  that  development 
should  not  be  forced  beyond  the  point  where  good  detail  is 
brought  out  in  dense  contrast.  One  minute  is  usually  sufficient. 

k.  Transfer  the  print  to  a  tray  containing  50  cu.cm.  of  cold 
clearing  solution.  After  two  or  three  minutes,  transfer  to  the 
rubber  tank  containing  the  usual  fixing  solution.  Fix  for  fifteen 
minutes  and  wash  for  one  hour. 

/.  Dry  the  prints  by  sponging  off  and  pinning  them  up  against 
a  table  edge  by  a  corner.  Leave  over  night,  and  then  flatten  out 
the  curl  with  an  electric  iron. 

Queries,  a.  Mount  the  better  print  on  a  standard  sized 
piece  of  cardboard  as  directed  by  the  instructions  accompanying 
the  Kodak  dry  mounting  tissue.  Note  below  the  print  the 
material,  magnification,  and  etching.  Name  the  various  struc- 
tural constituents  occurring  in  the  field,  and  indicate  their 
position  by  arrows. 

b.  How  does  the  appearance  of  the  constitution  of  the  alloy 
confirm  the  interpretation  of  the  cooling  curve  arrests  given  in 
Experiment  No.   10? 

c.  With  scissors  cut  the  crystalline  areas  from  the  eutectic 
on  the  other  print.     Weigh  both  groups  of  cuttings.     Assuming 
that  the  relative  proportion  of  each  constituent  by  volume  is 
proportional  to  the  area  exposed  at  any  such  random  plane,  figure 
the  composition  of  the  eutectic  from  the  weights  thus  determined. 
Discuss  any  discrepancies  observed. 

d.  State  briefly  the  chemistry  of  photography. 


EXPERIMENT  NO.  13 
HARDNESS 

Object.  The  object  of  this  experiment  is  to  determine  the 
hardness  of  various  metals. 

General  Explanation.  The  word  "  hardness  "  is  used  to 
express  various  properties  of  metals,  and  is  measured  in  as 
many  different  ways.  (See  Mills,  "  Materials  of  Construction/' 
pp.  323  and  459-) 

"  Scratch  hardness  "  is  used  by  the  geologist,  who  has  con- 
structed "  Moh's  scale  "  as  follows: 

Talc  has  a  hardness  of  i 

Rock  Salt  has  a  hardness  of  2 

Calcite  has  a  hardness  of  3 

Fluorite  has  a  hardness  of  4 

Apatite  has  a  hardness  of  5 

Feldspar  has  a  hardness  of  6 

Quartz  has  a  hardness  of  7 

Topaz  has  a  hardness  of  8 

Corundum  has  a  hardness  of  9 

Diamond  has  a  hardness  of  10 

A  mineral  will  scratch  all  those  above  it  in  the  series,  and  will 
be  scratched  by  those  below.  A  weighted  diamond  cone  drawn 
slowly  over  a  surface  will  leave  a  path  the  width  of  which 
(measured  by  a  micrometer  microscope)  varies  inversely  as  the 
scratch  hardness. 

"  Cutting  hardness  "  is  measured  by  a  standardized  drilling 
machine,  and  has  a  limited  application  in  machine  shop  practice. 

"  Rebounding  hardness  "  is  commonly  measured  by  the 
Shore  scleroscope,  illustrated  in  Fig.  12,  p.  98.  A  small  steeJ 

94 


HARDNESS  95 

hammer,  }  in.  in  diameter,  f  in.  in  length,  and  weighing  about 
iV  oz.  is  dropped  a  distance  of  10  in.  upon  the  test  piece.  The 
height  of  rebound  in  arbitrary  units  represents  the  hardness 
numeral. 

Should  the  hammer  have  a  hard  flat  surface  and  drop  on  steel 
so  hard  that  no  impression  were  made,  it  would  rebound  about 
90  per  cent  of  the  fall.  The  point,  however,  consists  of  a 
slightly  spherical,  blunt  diamond  nose  .02  in.  in  diameter, 
which  will  indent  the  steel  to  a  certain  extent.  The  work 
required  to  make  the  indentation  is  taken  from  the  kinetic 
energy  of  the  falling  body;  the  rebound  will  absorb  the  balance, 
and  the  hammer  will  now  rise  from  the  same  steel  a  distance  equal 
to  about  75  per  cent  of  the  fall.  A  permanent  impression  is 
left  upon  the  test  piece  because  the  impact  will  develop  a  force 
of  several  hundred  thousand  pounds  per  square  inch  under  the 
tiny  diamond-pointed  hammer  head,  stressing  the  test  piece  at 
this  point  of  contact  much  beyond  its  ultimate  strength.  The 
rebound  is  thus  dependent  upon  the  indentation  hardness,  for 
the  reason  that  the  less  the  indentation,  the  more  energy  will 
reappear  in  the  rebound;  also,  the  less  the  indentation,  the 
harder  the  material.  Consequently,  the  harder  the  material, 
the  more  the  rebound. 

"  Indentation  hardness  "  is  a  measure  of  a  material's  resist- 
ance to  penetration  and  deformation.  The  standard  testing 
machine  is  the  Brinell,  Fig.  13,  p.  99.  A  hardened  steel 
ball,  10  mm.  in  diameter,  is  forced  into  the  test  piece  with  a 
pressure  of  3000  kg.  (or  1000  kg.  for  soft  metals  such  as  copper, 
aluminum  and  white  metals) .  The  resulting  indentation  is  then 
measured. 

While  under  load,  the  steel  ball  in  a  Brinell  machine  naturally 
flattens  somewhat  into  a  spheroidal  shape.  The  indentation  left 
behind  in  the  test  piece  is  a  duplicate  of  the  surface  which  made 
it,  and  is  usually  regarded  as  being  the  segment  of  a  sphere  of 
somewhat  larger  radius  than  that  of  the  unstressed  spherical 
ball.  The  radius  of  curvature  of  this  spherical  indentation  will 
vary  slightly  with  the  load  and  the  depth  of  indentation.  The 


96  EXPERIMENTAL  GROUP  III 

Brinell  hardness  numeral  is  the  quotient  found  by  dividing  the 
test  pressure  in  kilograms  by  the  spherical  area  of  the  indenta- 
tion. The  denominator,  as  before,  will  vary  according  to  the 
size  of  the  sphere,  the  hardness  of  the  sphere  and  the  load. 
These  items  have  been  standardized,  and  tables  for  each  machine 
have  been  constructed  so  that  if  the  diameter  of  the  circular 
identation  produced  by  a  load  of  3000  kilograms  be  measured, 
the  hardness  numeral  may  be  taken  out  directly. 

Since  the  scleroscope  number  is  also  dependent  to  a  certain 
extent  upon  the  resistance  to  indentation,  it  should  have  a  definite 
ratio  to  the  Brinell  number  for  the  same  kind  of  metals.  Tests 
show  that,  very  approximately,  the  Brinell  number  may  be  had 
from  the  scleroscope  number  by  multiplying  the  latter  by  certain 
numbers,  somewhat  as  follows: 

Hardened  tool  steel 6.0 

Hot  rolled  mild  steel 5.6  scleroscope +14 

Gray  cast  iron 5.8 

Etc. 

Since  there  is  a  flow  of  metal  from  the  overstrained  portion 
immediately  under  the  Brinell  ball  during  the  test,  there  should 
be  a  relation  between  the  hardness  and  the  ultimate  strength. 
This  is  shown  graphically  in  Fig.  271,  p.  462,  of  Mills,  "  Materials 
of  Construction."  The  Bureau  of  Standards'  Technologic 
Paper  No.  n  shows  that  if  the  depth  of  the  indentation  be  meas- 
ured, the  hardness  numeral  derived  will  be  independent  of  the 
size  and  hardness  of  the  sphere.  If,  then,  the  depth  of  the 
depression  be  measured  we  can  compute,  in  pounds  per  square 
inch, 

Load  in  kg. 


Ultimate  strength  =  20,000+10.32 


Depression  in  millimeters. 


This  formula  will  give  results  to  within  5  per  cent  for  steels  of 
quite  various  compositions.  For  other  classes  of  materials,  the 
constants  will  be  different. 

The  limitations  of  the  Brinell  method  are  bounded  by  the 


HARDNESS  97 

hardness  of  the  steel  ball.  The  cold  working  of  the  metal  under 
the  ball  affects  the  hardness  of  the  specimen  at  the  point  tested. 
The  indentations  left  behind  preclude  its  use  on  finished  sur- 
faces. The  mass  of  material  required  for  testing  is  considerable. 
The  machine  is  not  portable.  The  last  two  limitations  have 
been  removed  by  the  so-called  "  Brinell  Meter." 

On  the  other  hand,  the  results  of  tests  by  the  Shore  sclero- 
scope  depend  to  a  larger  extent  upon  the  personal  equation  of  the 
operator,  and  the  method  of  mounting  the  specimens;  it  is  a  non- 
recording  instrument;  it  is  incapable  of  adjustment;  and  it  is 
worthless  for  soft  alloys. 

Special  Apparatus.  The  special  apparatus  required  is  as 
follows: 

Spirit  level. 

Millimeter  scale. 

Magnifying  glass. 

One  inch  square  bar  of  each  of  the  following  metals: 

Aluminum,  marked  Al. 

Copper,  marked  Cu. 

Tobin  bronze  (90  per  cent  Cu,   10  per  cent  Sn) 

marked  Br. 

White  cast  iron,  not  marked. 
Gray  cast  iron,  marked  GCI. 
Wrought  iron,  marked  WI. 
High  carbon  steel,  marked  STEEL. 

Two-inch  length  of  worn  railroad  rail. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Shore  scleroscope. 
Brinell  testing  machine. 
Micrometer  microscope. 

Directions  for  the  Use  of  Scleroscope.  Fig.  12.  i.  Set 
the  instrument  plumb  by  adjusting  the  leveling  screws  K  until 


98 


EXPERIMENTAL  GROUP  III 


k 


the  loose  side-rod  /,  acting  as  a  plumb  bob,  hangs  freely  in  the 
center  of  the  ring  at  its  lower  end. 

2.  Smooth  the  surface  of  the  point  to  be  tested,  removing 
any  scale  or  rust. 

3.  Level  the  point  to  be  tested,  mounting  the  piece  solidly 

in  a  vise  or  between  the  spheri- 
cal anvil  and  the  foot  L.  In  the 
latter  case,  maintain  a  slight 
pressure  on  the  lever  M  at  all 
times.  Lower  the  barrel  N  upon 
the  upper  part  of  the  foot  L  by 
means  of  the  knob  O. 

4.  Release   the   hammer  by 
squeezing  the  bulb  A,  and  note 
the  approximate  height  of  the 
first  rebound.     Arrange  the  light 
so  that  it   glistens   against  the 
top  of  the  hammer.     Raise  the 
hammer  by  again    compressing 
the  bulb  A  and  then  releasing 
quickly. 

5.  Move  the  test  piece  slight- 
ly so  that  the  hammer  will  not 
fall  in  exactly  the  same  place, 
and  remount  as  in  3. 

6.  Fix  your  vision  upon  the 
scale  a  few  divisions  below   the 
approximate   rebound  mentally 
noted  in  4,  and  read  the  exact 

reached   by   the 


FIG.  12. — Shore  Scleroscope. 


scale  number 
top  of  the  hammer  on  its  second  release. 

7.  Repeat  5  and  6  until  three  concordant  readings  are  found, 
the  average  of  which  will  represent  the  hardness  of  the  piece 
tested. 

8.  Test  the  standard  bar  in  the  instrument  case  in  order  to 
obtain  a  conversion  factor  for  the  observations. 


HARDNESS 


99 


Direction  for  Making  the  Brinell  Ball  Test.     i.  Smooth  the 
surface  to  be  tested,  removing  any  scale  or  rust. 

2.  Place  the  test  piece  upon  the  anvil  A,   Fig.  13,  leveling 


FIG.  13. — Hydraulic  Testing  Machine.     (Brinell  Principle.) 

by  means  of  the  spherical  joint  and  the  spirit  level.     Raise  up 
to  contact  with  the  ball  B  by  the  hand  wheel  C. 

3.  Close  the  valve  D  and  pump  oil  slowly  behind  the  piston 
with  the  hand  lever  E,  noting  the  increase  of  pressure  on  the  gage, 
and  continue  until  the  yoke  F  floats. 


100 


EXPERIMENTAL   GROUP  III 


4.  Maintain    pressure    15    seconds   with    a    30oo-kg.    load, 
or  30  seconds  with  a  looo-kg.  load.     Release  by  opening  valve  D. 
Unscrew  the  hand  wheel  C. 

5.  Estimate   the   diameter  of   the  impression   to   o.i    mm. 
with   a  key-seat  scale  and  magnifying   glass,   taking  out  the 
corresponding  hardness  numeral  from  the  accompanying  tabula- 
tion.     Use   one- third   the   hardness  given  when   testing  with 
1000  kg. 

TABLE  FOR  BRINELL  BALL  TEST 


t 

Diameter  of  Ball 
Impression,  mm. 

Hardness  Number 
for  a  Load  of 
3000  kg. 

Diameter  of  Ball 
Impression,  mm. 

Hardness  Number 
for  a  Load  of 
3000  kg. 

2.0 

946 

4-5 

1/9 

2.  1 

857 

4-6 

170 

2.  2 

782 

4-7 

l63 

2-3 

713 

4-8 

156 

2-4 

652 

4-9 

149 

2-5 

600 

5-o 

J43 

2.6 

555 

5-i 

137 

2.7 

512 

5-2 

J3i 

2.8 

477 

5-3 

126 

2.9 

444 

5-4 

121 

3-o 

418 

5-5 

116 

3-i 

387 

5-6 

112 

3-2 

364 

5-7 

107 

3-3 

340 

5-8 

103 

3-4 

321 

5-9 

99 

3-5 

302 

6.0 

95 

3-6 

286 

6.1 

92 

3-7 

269 

6.2 

89 

3-8 

255 

6-3 

86 

3-9 

241 

6.4 

82 

4-0 

228 

6-5 

80 

4-i 

217 

6.6 

77 

4.2 

207 

6-7 

74 

4-3 

196 

6.8 

71-5 

4-4 

187 

6-9 

69 

HARDNESS  '  101 

NOTE:  The  oil  used  in  the  Brinell  machine  is  a  mixture 
of  half  heavy  cylinder  oil  and  half  light  engine  oil.  After  each 
test,  the  piston  rod  G  should  be  driven  upward  by  pressure  from 
the  screw  and  hand  wheel  C  (using  a  piece  of  scrap  metal  to  pro- 
tect the  anvil)  to  return  the  oil  to  the  lower  side  of  the  plunger. 

Procedure,  a.  Test  the  standard  bar  under  the  scleroscope, 
and  compute  a  conversion  factor  for  subsequent  readings. 

b.  Test  the  hardness  of  all  the  metallic  specimens  by  both 
the   scleroscope   and   the   Brinell  machine.     Construct  a  neat 
tabulation  giving  the  results  arranged  in  the  order  of  increasing 
hardness  and  figure  the  ratio  between  the  two  hardness  numbers 
for  each  material. 

c.  Examine  the  ball  impression  in  the  wrought  iron  under  the 
micrometer  microscope,  measuring  the  diameter  accurately  both 
with  and  across  the  direction  of  rolling. 

d.  Explore  the  hardness  of  the  rail  surface  and  cross-section 
with  the  scleroscope,  and  map  the  results. 

Queries,  a.  Should  a  constant  relation  exist  between  the 
Brinell  and  Shore  numerals?  Give  reasons  for  your  opinion. 

b.  Discuss  the  reasons  for  any  variation  in  hardness  found 
at  different  points  in  the  rail. 

c.  Why  should  an  elliptical  depression  be  left  when   the 
side  of  a  rolled  bar  be  tested?     Explain  the  results  of  procedure  c. 

d.  If  5.57  mm.  is  the  mean  radius  of  curvature  of  the  sphe- 
roidal depression,  what  angle  is  subtended  at  the  center  by  the 
mean  diameter  of  the  indentation  in  the  merchant  bar? 

c.  What  is  the  area  of  the  depression? 

/.  What  is  the  depth  of  the  depression? 

g.  What  is  the  ultimate  strength  of  the  bar? 

h.  Figure  the  Brinell  number  for  this  bar  without  reference 
to  the  table  given  above. 

i.  How  can  the  radius  of  curvature  of  the  spheroidal  depres- 
sion be  determined  experimentally? 

/.  How  can  the  depth  of  the  depression  be  determined  ex- 
perimentally? 


EXPERIMENT  NO.  14 
ELECTRIC  FURNACES 

Object.  The  object  of  this  experiment  is  to  construct  a 
wire-wound  pot  furnace. 

General  Explanation.  When  an  electric  current  passes  along 
a  wire  or  other  conductor  it  can  be  found  that  while  the  amount 
of  current  (amperes)  is  the  same  at  the  end  as  at  the  start, 
its  potential  or  "  head  "  (voltage)  is  decreased.  This  is  a  direct 
deduction  from  Ohm's  law  as  given  in  Experiment  No.  6  (q.v.) 
which  may  be  symbolized  as 

c-f, 

or,  transposing, 

II.  E  =  CR. 

In  words,  the  drop  in  potential,  or  "  loss  in  head,"  varies  as  the 
product  of  the  current  by  the  resistance. 

The  energy  lost  during  this  drop  in  potential  is  that  amount 
required  to  overcome  the  resistance  offered  by  the  conductor 
to  the  passage  of  the  current,  and  reappears  as  heat  in  the 
conductor.  The  unit  of  electrical  energy  is  the  Joule,  and  is 
equal  to  the  work  done  during  one  second  while  a  current  of 
one  ampere  falls  thru  a  difference  of  potential  of  one  volt. 
The  work  done  during  the  passage  of  an  electrical  current  is, 
therefore, 

Joules  =  voltage  drop  X  current  passing  X  time ; 
or,  in  symbols, 

III.  J  =  ECt. 

102 


ELECTRIC  FURNACES  103 

But,  by  Equation  II,  the  drop  in  potential  E  is  equal  to  CR. 
Substituting  this  value  in  III 

IV.  J  =  CR-Ct  =  C2Rt. 

Equation  IV,  expressing  the  amount  of  work  done  by  the 
passage  of  any  current  thru  some  resistance  for  a  measured 
length  of  time,  can  be  transformed  into  heat  units  by  use  of  the 
mechanical  equivalent  of  heat.  Thus,  one  Joule  is  equivalent 
to  io7  ergs,  while  it  has  been  determined  that  one  calory  is 
equivalent  to  4.i89Xio7  ergs.  Hence  by  proportion, 

io7  ergs  . 

i  Joule  =  — —  calories 

4.189X10'  ergs 

=  0.24  calories. 
Substituting  this  value  in  Equations  III  and  IV,  we  have 

V.  Heat,  in  calories  =  0.24  ECt 

VI.  =0.24  C2RL 

The  generation  of  heat  by  electricity  according  to  the  above 
principles  is  naturally  more  costly  than  by  carbonaceous  fuel, 
inasmuch  as  the  electrical  energy  is  usually  produced  from  fuel 
thru  the  intermediation  of  costly  boilers,  engines,  generators, 
transmission  lines,  and  transformers,  each  of  which  operates  at 
less  than  100  per  cent  efficiency.  An  electric  furnace  would 
seldom  be  installed,  therefore,  unless  it  offered  advantages  which 
outweigh  the  increased  heat  cost  per  calory.  Thus,  small 
laboratory  furnaces  are  cleaner,  more  easily  controlled,  and  more 
uniform  in  temperature  than  carbon  fired  furnaces. 

Certain  smelting  operations,  on  the  other  hand,  require  -a 
temperature  higher  than  the  maximum  obtainable  with  carbon- 
aceous fuel  (1600  to  1900°  C.).  As  shown  in  Appendix  A,  these 
temperatures  are  limited  by  the  point  where  the  escaping  prod- 
ucts of  combustion  carry  away  as  sensible  heat  all  the  calories 
generated  by  the  chemical  reaction.  At  this  point,  of  course, 
the  efficiency  of  the  furnace  becomes  zero,  as  there  is  no  surplus 


104  EXPERIMENTAL  GROUP  III 

of  heat  left  for  useful  purposes.  In  fact,  the  flow  of  heat  from  the 
source  to  the  absorber  by  conduction  varies  as  the  difference  in 
temperature  between  the  two,  and  consequently  if  any  consider- 
able amount  of  heat  is  to  be  absorbed  by  the  furnace  charge, 
the  heating  elements  or  source  should  uniformly  have  a  much 
higher  temperature  than  that  required  by  the  process  going 
forward  within.  This  can  be  readily  obtained  by  electrical 
means,  the  upper  limits  of  temperature  being  dependent  only 
upon  the  destruction  of  the  refractories  forming  the  furnace 
itself.  Other  processes  requiring  close  control  of  a  neutral 
atmosphere,  or  an  absence  of  carbon,  oxygen,  or  nitrogen  are 
proper  fields  for  electric  furnace  operation. 

A  great  variety  of  electric  furnaces  have  been  constructed  or 
proposed,  but  in  every  case  the  heating  is  effected  by  the  passage 
of  current  thru  a  resistor.  Thus,  the  various  types  of  arc 
furnaces  (Mills,  "  Materials  of  Construction,"  pp.  400-403) 
generate  heat  mainly  by  the  passage  of  a  relatively  small  current 
across  an  air  gap  having  a  very  high  resistance.  The  induction 
furnace  (loc.  cit.,  pp.  404-406),  on  the  other  hand,  is  a  trans- 
former which  produces  within  itself  enormous  currents  in  a  metal 
bath,  which  forms  a  secondary  winding  of  very  low  resistance. 
Between  these  extremes  may  be  placed  the  so-called  "  resistance" 
furnace  (loc.  cit.,  pp.  288,  289),  which  generates  heat  by  a  passage 
of  a  moderate  current  thru  a  material  of  moderate  resistance. 
The  resistor  in  this  case  may  be  the  furnace  charge  itself,  as 
in  the  ore  smelting,  carborundum  or  graphite  furnaces;  or 
it  may  be  wound  or  packed  around  the  furnace  walls,  as  is  the 
case  of  laboratory  muffle  or  tube  furnaces.  For  a  description 
of  the  design,  construction  and  use  of  these  furnaces,  the  student 
is  referred  to  "  The  Electric  Furnace,"  by  Alfred  Stansfield. 

In  the  present  state  of  our  knowledge,  a  precise  mathematical 
treatment  of  furnace  design  is  impossible,  not  so  much  from 
ignorance  of  the  underlying  principles  of  heat  transfer,  as  from 
a  dearth  of  physical  constants.  Thus,  we  will  suppose  that  a 
certain  chemical  reaction  is  proceeding  in  a  continuous  electric 
furnace  whose  energy  input  is  known.  It  is  very  simple  to 


ELECTRIC  FURNACES  105 

figure  the  amount  of  heat  liberated  in  the  furnace  from  the 
readings  of  an  ammeter  and  a  voltmeter.  But  where  does 
'this  heat  go?  A  part  is  used  in  heating  the  furnace  charge  to 
the  temperature  of  the  escaping  products,  which  can  be  com- 
puted if  the  specific  heats  of  the  various  items  of  the  furnace 
charge  is  known.  A  part  may  be  absorbed  by  an  endothermic 
chemical  reaction,  which  also  may  be  computed  if  we  know  the 
thermochemical  constants  of  the  equations,  likewise  as  shown 
in  Appendix  A.  A  much  larger  part  escapes  thru  the  furnace 
walls  and  is  wasted.  The  inner  surface  of  the  walls  receive 
heat  by  conduction  and  radiation  from  the  hot  bath  and  furnace 
atmosphere;  this  heat  is  transferred  to  the  outer  surface  by 
conduction,  and  is  there  dissipated  by  conduction  to  the  air  and 
the  furnace  foundation,  by  convection  of  air  currents,  and  by 
radiation  thru  the  ether  into  the  cooler  surroundings. 

The  transfer  of  heat  by  conduction  thru   a  solid  may  be 
computed  by  the  formula 


where  Wc  =  calories  transferred  per  second  by  conduction  from 

one  square  centimeter  of  the  surface; 
S  =  factor  depending  upon  the  shape  of  the  conducting 
mass   (see  Langmuir,   24  Trans.  Electrochemical 
Society,  53); 
r  =  thermal  resistivity  of  the  solid  body,  or  the  coef- 

ficient of  transfer  across  an  interface; 
Th  =  temperature  of  the  hot  side  in  degrees  Cent.  ; 
Tc  =  temperature  of  the  cold  side,  in  degrees  Cent. 

The  transfer  of  heat  by  convection  may  be  figured  by  the 
above  formula  if  the  thermal  resistivity  be  replaced  by  a  factor 
called  the  coefficient  of  internal  transfer,  which  depends  upon  the 
nature  of  the  surrounding  iluid  and  its  velocity.  Richards,  I 
"  Metallurgical  Calculations  "  178,  develops  this  method.  Lang- 
muir, 23  Trans.  Electrochemical  Society,  299,  presents  a  new 
conception  of  this  action. 


106  EXPERIMENTAL   GROUP  III 

The   transfer  of  heat  by  radiation   can   be   computed   by 
Stefan's  law: 


Where  Wr  =  calories  transferred  per  second  by  radiation  from  one 

square  centimeter  of  the  surface; 
E  =  emissivity  ,  a  factor  depending  upon  the  nature  of  the 

radiating  surface; 
Kh  =  absolute  temperature  (metric  scale)  of  the  radiating 

body; 

Kc  =  absolute  temperature  (metric  scale)  of  the  absorbing 
body; 

These  formulas  evidently  require  for  their  applications  a 
good  knowledge  of  the  shape  factor,  specific  resistivity,  surface 
resistance  and  emissivity,  all  of  which  may,  and  perhaps  do, 
vary  somewhat  with  the  temperature  as  well  as  with  the  chemical 
composition  and  physical  constitution  of  the  substances  in  ques- 
tion. An  unlimited  field  for  experimental  research  is  here  open, 
as  our  present  knowledge  of  these  constants  is  poor  indeed,  and 
the  technical  importance  of  the  information  is  obvious.  On 
account  of  this  paucity  of  information,  furnaces  are  not  "  de- 
signed "  in  the  true  sense  of  the  word,  but  grow  as  a  result  of 
"  cut  and  try  "  processes. 

It  has  been  found,  for  instance,  that  a  small  laboratory 
tube  furnace  will  heat  up  quite  rapidly  with  a  current  of  10 
amperes.  After  once  reaching  a  high  heat,  the  current  should  be 
cut  down  to  balance  radiation  and  other  losses.  If,  therefore, 
the  winding  be  made  of  a  length  of  wire  with  a  total  resistance 
of  10  ohms  and  an  external  resistance  (rheostat)  giving  from  o 
to  20  ohms  be  placed  in  series  with  the  furnace  across  the  usual 
no-  volt  lighting  circuit,  any  current  from  4  to  n  amperes 
may  be  impressed  at  the  will  of  the  experimenter.  Lesser  cur- 
rents may  evidently  be  had  by  further  increasing  the  external 
resistance.  A  cross-sectional  view  of  the  proposed  furnace  is 
shown  in  Fig.  14. 


ELECTRIC   FURNACES 


107 


Tube  furnaces  may  be  arranged  to  give  a  uniform  temperature 
from  end  to  end  by  using  heat  conducting  ends  of  metal,  as 
described  by  A.  W.  Gray,  in  10,  United  States  Bureau  of 
Standards'  Bulletin,  460. 


%  Transite  Board 


24  Gage  Galvanized 
Iron 


Brass  Binding 
Post 


18  Gage  "Rayo"  Wire 


tap  •••.*?//. 

^Kieselguhr  Packing  '  1  / 

i»x' .'-„ : t >v  c(  v 


k  •   v  _/ 1 -^  v  -Vv    V"- '£.  ~~  I  1<x  %  bent 

^fr^^^^^^^^^Sto^Bdlli,' 
5^  long 


10  Square- 


npie<;e 


FIG.  14. — Wire-wound  Pot  Furnace. 


Special    Apparatus.     The     special    apparatus    used    is    as 
follows: 

Can  of  alundum  cement. 

Spatula. 

Spool  of  asbestos  tape. 

Tinners'  snips. 

Screw  punch,  with  die  for  f-in.  hole. 

Eight-inch  gas  pipe,  12  in.  long. 

Carpenter's  handsaw. 

Jig  saw. 

Round  rasp. 


108  EXPERIMENTAL  GROUP  III 

Supplies.     The  supplies  needed  are  as  follows: 

One  corrugated  alundum  core,  No.  6597. 

Three  feet  of  asbestos  string. 

Sheet  of  24-gage  galvanized  iron. 

Transite  board. 

Eight  f-in.  stove  bolts,  f  in.  long. 

Two  brass  binding  posts. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Core  oven  at  80°  C. 

Sack  of  kieselguhr. 

Drill  press,  with  f-,  f-,  and  |-in.  drills. 

Soldering  outfit,  including 

Soldering  tool, 

Soldering  paste, 

Solder, 

Piece  of  cloth  for  wiping. 

Procedure,  a.  Compute  the  length  of  resistance  wire  re- 
quired to  wind  the  corrugated  core,  and  obtain  same  from  the 
stock-room. 

b.  Wind  the  wire  tightly  about  the  core,  being  careful  to 
place  the  wire  in  the  bottom  of  the  corrugation,  equally  spaced 
thruout.      Fasten    the   end    turns   with    asbestos    string,    and 
plaster  the  corrugations  smooth  with  alundum  cement. 

c.  Wind  the  core  closely  up  and  down  with  asbestos  tape, 
and  tie  the  ends.     Place  in  a  core  oven  at  80°  C.  for  two  hours. 

d.  Cut  a  piece  of  galvanized  sheet  to  make  the  outer  casing, 
bend  it  around  a  short  piece  of  8-in.  pipe,  and  solder  the  edges 
together  as  instructed  in  Experiment  No.  6,  p.  45.     Cut  eight 
pieces  of  sheet,  i  in.  by  f  in.,  bend  into  an  angle,  and  punch  a 
f-in.  hole  in  one  leg.     Solder  these  angles  at  the  quarter  points 
of  the  top  and  bottom  edges  for  end  attachment. 

e.  Saw  two  pieces  of  transite  board,  10  in.  square,  and  one 
piece  5  in.  square.     Lay  out  the  necessary  holes  for  the  end  con- 


ELECTRIC   FURNACES 


109 


nections,  binding  posts  and  wire  outlets.  Bore  these  in  a  drill 
press,  using  a  heavy  feed.  Cut  a  round  hole  in  the  top  slightly 
larger  than  the  core. 

/.  Attach  the  galvanized  iron  casing  to  the  top- by  stove  bolts, 
set  the  dried  core  in  place,  and  pack  tightly  with  kieselguhr. 
Then  bolt  on  the  base,  and  connect  and  solder  resistance  wires 
to  the  binding  posts. 

g.  For  operating,  connect  to  the  source  of  current  as  shown 
in  the  following  diagram,  Fig.  15.  The  first  heating  should  be 
very  slow,  to  properly  season  the  alundum  cement. 


110  Volt  Line. 


20-Ohm  Rheostat 


FIG.  15. — Wiring  Diagram  for  Wire- wound  Furnace. 

Queries,  a.  If  an  electric  furnace  has  a  resistance  of  7 
ohms,  and  is  connected  across  a  2 20- volt  line  by  325  feet  of  wire 
with  0.007  onm  Per  f°°t  resistance,  how  much  current  will 
flow  thru  the  furnace?  How  much  current  will  pass  thru  the 
leads?  How  many  Joules  will  pass  thru  the  furnace  in  one 
hour?  How  much  heat  will  be  generated  in  the  furnace  per 
second? 

b.  Classify  and  distinguish  the  various  kinds  of  electric  fur- 
naces according  to  their  electrical  characteristics. 

c.  If  an  electrical  horse-power  is  equal  to  746  watts,  and 
costs  $15.00  per  year  in  large  quantities,  compare   the  cost  of 


110  EXPERIMENTAL   GROUP  III 

heat  generated  electrically  with  that  furnished  by  the  combus- 
tion of  one  of  the  coals  discussed,  in  Appendix  A,  should  the 
latter  cost  $3.00  per  ton. 

d.  What  is  the  maximum  temperature  which  may  be  obtained 
in  resistance  furnaces? 

e.  A  bar  of  tool  steel,  3  cm.  by  3  cm.  by  10  cm.  is  drawn 
from  a  furnace  at  1000°  C.  and  cools  in  still  air  at  20°  C.     If 
the  emissivity  of  the  iron  oxide  covering  the  bar  is  0.9,  how  much 
heat  is  radiated  per  second?    Assuming  this  rate  to  remain 
unchanged  for  one  minute,  what  is  the  then  temperature  of  the 
bar,  if  its  specific  heat  is  0.179  calories  per  gram  and  its  specific 
gravity  is  7.7? 

/.  Suppose  it  is  desirable  to  use  the  furnace  made  in  this 
experiment  in  a  certain  investigation  requiring  a  uniform  tem- 
perature of  1000°  C.  Outline  an  experiment  to  enable  one  to 
predict  the  current  required  to  bring  the  cold  furnace  up  to 
equilibrium  at  exactly  1000°  C. 

g.  What  is  the  difference  between  the  construction  of  a 
voltmeter  and  an  ammeter? 


EXPERIMENT  NO.  15 
RADIATION  AND  OPTICAL  PYROMETERS 

Object.  The  object  of  this  experiment  is  to  become  accus- 
tomed to  the  use  of  the  various  styles  of  radiation  and  optical 
pyrometers. 

General  Explanation.*  The  temperature  of  hot  bodies  may 
be  estimated  by  measuring  the  radiant  energy  emitted  in  the 
form  either  of  visible  light  radiation  or  of  the  longer  infra- 
red, non-luminous  rays.  In  any  case,  optical  or  radiation 
pyrometers  utilize  the  relation  between  total  radiation  and 
temperature  expressed  by  Stefan's  law  (p.  106) : 


Where  WT  =  calories  transferred  per  second  by  radiation  from 

one  square  centimeter  of  surface; 
E  =  emissivity ,  a  factor  depending  upon  the  nature  of  the 

radiating  surface; 
Kh  =  absolute  temperature  (metric  scale)  of  the  radiating 

body; 

and        Kc  =  absolute  temperature  (metric  scale)  of  the  absorb- 
ing body. 

Radiation  Pyrometers 

When  we  consider  the  enormous  increase  in  the  intensity  of 
radiation  with  rise  in  temperature,  this  method  appears  especially 
well  adapted  to  the  measurement  of  high  temperatures.  This, 
however,  is  only  partly  true;  the  method  is  limited  somewhat 


*  These    notes    have     been    abstracted     in   part    verbatim    from   Burgess* 
"  Measurement  of  High  Temperatures,"  Chapters  VI  to  VIII. 

Ill 


112  EXPERIMENTAL  GROUP  III 

by  the  fact  that  different  bodies,  altho  at  the  same  tem- 
perature, emit  vastly  different  amounts  of  light  and  heat  owing 
to  the  fact  that  the  emissivity  factor  is  different  for  different 
substances,  and  (for  that  matter)  often  varies  with  the  tempera- 
ture. 

Kirkhoff,  in  one  of  the  most  important  contributions  to  the 
theory  of  radiation,  was  led  to  the  important  conception  of  what 
he  termed  a  a  black  body."  He  denned  this  as  one  which  would 
absorb  all  radiations  falling  upon  it,  and  would  neither  reflect 
nor  transmit  any.  While  carbon  and  iron  oxide  approximate 
black  body  radiation  with  an  emissivity  factor  approaching 
unity,  a  " theoretical  black  body"  may  be  attained  experimentally 
by  constructing  an  enclosed  space,  all  parts  of  which  are  main- 
tained at  the  same  temperature. 

Precise  calibration  of  radiation  and  optical  pyrometers  may 
then  be  made  by  observing  the  radiation  emitted  thru  a 
small  opening  in  the  walls  of  some  vessel  plunged  in  a  constant 
temperature  bath,  or  enclosed  in  a  uniformly  heated  tube  .fur- 
nace. The  temperature  of  the  interior  of  this  radiator  may 
be  ascertained  at  the  same  time  with  a  calibrated  platinum 
thermo-couple,  and  thus  a  correlation  established  between  radi- 
ation and  known  temperature.  Such  work,  however,  is  beyond 
the  scope  of  elementary  practice,  and  transcends  the  facilities 
of  an  ordinary  laboratory;  consequently  such  calibration  should 
usually  be  intrusted  to  the  Bureau  of  Standards. 

An  enclosed  room  with  uniformly  heated  walls  absorbs  like 
a  theoretical  black  body — that  is  to  say,  perfectly — because  any 
portion  of  a  heat  wave  not  absorbed,  but  reflected,  on  the  first 
impingement,  would  ultimately  be  absorbed  during  subsequent 
reflections.  Further,  bodies  in  equilibrium  with  their  surround- 
ings must  absorb  and  radiate  heat  at  exactly  the  same  rate; 
otherwise,  should  the  absorption  be  greater  than  the  radiation, 
a,  body  would  spontaneously  increase  in  temperature  without 
limit.  Therefore,  a  furnace  of  crucible  or  any  other  enclosure 
whose  walls  and  contents  are  at  a  uniform  temperature  has  unit 
emissivity,  no  matter  of  what  material  it  is  constructed. 


RADIATION  AND   OPTICAL   PYROMETERS 


113 


For  this  reason,  the  variation  in  emissivity  with  matter  and 
temperature  is  really  a  consideration  of  much  less  importance, 
inasmuch  as  a  bath  of  steel  in  a  hot  furnace  radiates  at  nearly 
a  theoretical  black-body  rate.  It  is  important  to  limit  this 
statement  to  furnaces  which  have  reached  approximate  equilib- 
rium, and  are  not  obscured  by  flames,  which  are  always  hotter 
than  the  furnace.  It  is  apparent,  therefore,  that  metal  in  a 
furnace  will  appear  much  hotter  to  optical  and  radiation  pyr- 
ometers than  the  same  metal  immediately  thereafter  on  being 
tapped  from  the  furnace,  and  passing  thru  cold  air. 


Front  View. 


Sectional  Elevation. 
FIG.  1  6.  —  Fery  Pyrometer. 


The  Fery  pyrometer  (Fig.  16)  was  the  first  convenient  form 
of  instrument  making  use  of  total  radiation  and  based  on  Stefan's 
law.  In  this  instrument,  the  radiation  from  an  incandescent 
body  is  focused  thru  a  lens  or  by  a  concave  mirror  (M) 
upon  a  very  sensitive  thermo-couple  junction  (F)  and  raises  its 
temperature.  The  electromotive  force  thus  generated  actuates 
a  sensitive  galvanometer  in  series  with  the  couple  in  exactly 
the  same  way  as  discussed  in  Experiment  No.  6.  This  is  there- 
fore a  radiation  pyrometer  which  is  direct  reading  by  means  of  a 
pointer  on  a  scale,  and  may  readily  be  made  into  a  recording 
instrument. 


114  EXPERIMENTAL  GROUP  III 

In  making  a  temperature  measurement,  it  is  necessary  to 
sharply  focus  the  image  of  the  incandescent  object  upon  the 
thermo-junction  by  an  ingenious  device  by  means  of  which 
straight  lines  appear  broken  unless  the  instrument  is  in  focus 
(Fig.  17).  The  range  of  the  instrument  is  increased  by  means 
of  a  sectored  diaphragm  (D,  Fig.  16),  so  that  temperatures  from 
the  lowest  to  the  highest  may  be  read,  altho  for  low  tem- 
peratures, a  quite  sensitive  galvanometer  is  needed. 

It  should  be  emphasized  that  in  general,  radiation  pyrom- 
%eters  sighted  upon  objects  in  the  open  air  will  read  too  low  in 
temperature,  due  to  the  selective  radiating  properties  of  all 
materials.  They  may  be  calibrated  to  give  true  surface  tem- 
peratures when  sighted  upon  any  substance  whose  radiating 


Focus. 
FIG.  17. — Focusing  Scheme  for  Fery  Pyrometer. 

properties  are  known,  and  in  any  case,  a  consistent  but  arbi- 
trary scale  is  obtained  so  long  as  the  surface  sighted  upon  does 
not  change  its  emissivity.  Flames  and  furnace  gases,  which  also 
seriously  affect  the  readings  of  such  pyrometers,  may  also  be 
avoided,  togethe^  with  the  'selective  radiation  errors,  by  sight- 
ing on  the  bottom  of  a  closed-end  tube  inserted  into  the  furnace. 
The  radiation  from  such  a  tube  of  fire-clay  or  other  refractory 
will  approach  closely  to  the  ideal  black  body  conditions  under 
which  radiation  instruments  will  read  correctly.  The  radiation 
laws  in  their  simplest  form  apply  exactly  to  such  a  radiating 
tube,  so  that  if  the  pyrometc.  has  been  calibrated  for  theoretical 
black  body  radiation,  the  readings  will  hold  when  sighting  into 
such  a  tube,  or  thru  a  small  aperture  into  any  clear,  closed 
space  at  constant  temperature. 


RADIATION  AND  OPTICAL  PYROMETERS  115 

Optical  Pyrometers 

Instead  of  using  the  totality  of  the  radiant  energy,  as  in  the 
method  described  above,  optical  pyrometers  make  use  of  some 
part  of  the  luminous  radiations  only.  A  discussion  of  the  laws  of 
radiation,  as  applied  to  waves  of  various  lengths,  would  be  out 
of  place  in  an  elementary  book,  and  therefore  only  the  following 
general  principles  and  deductions  are  presented. 

An  incandescent  body  emits  radiations  of  different  wave 
lengths.  The  intensity  of  this  emitted  radiation  is  not  the  same 
for  different  bodies,  even  for  a  given  wave  length,  and  a  given 
temperature.  This  fact  is  expressed  in  other  words  by  saying 
that  different  materials  have  different  emissive  powers,  for  a 
given  radiation.  Similarly,  a  body  which  receives  radiations  of  a 
given  wave  length  absorbs  part  of  them  and  sends  back  another 
part  by  diffusion  or  reflection;  a  certain  quantity  may  also  trav- 
erse the  body.  Therefore,  the  diffusing,  reflecting,  transmit- 
ting, or  emissive  power  at  a  given  temperature,  and  for  a  given 
wave  length,  varies  from  one  body  to  another. 

It  follows  from  this  that  the  relative  proportions  of  the 
various  visible  radiations  received  or  given  off  by  a  body  are  not 
the  same;  and  that  different  bodies,  at  the  same  temperature, 
appear  to  be  differently  colored.  At  temperatures  less  than 
2000°  C.  the  long  wave  lengths  in  the  emitted  light  predominate 
greatly,  and  the  red  colorations  they  produce  mask  the  inequali- 
ties of  the  radiations  of  other  wave  lengths.  To  render  the 
colorations  of  radiating  bodies  easily  visible,  it  is  necessary  to 
compare  them  with  those  of  a  theoretical  black  body  under  the 
same  temperature  conditions.  A  hole  pierced  in  the  body,  or 
a  crack  across  the  surface,  gives  a  very  good  term  of  comparison 
to  judge  of  this  coloration. 

The  intensity  of  the  radiations  emitted  by  a  theoretical 
black  body  always  increases  with  the  temperature,  and  the  rate 
of  change  is  the  more  rapid  as  it  approaches  the  blue  region  of 
the  spectrum;  but,  on  the  other  hand,  the  radiations  from  the 
red  end  are  the  first  to  have  an  intensity  sufficient  to  affect  the 


116  EXPERIMENTAL  GROUP  III 

eye.  The  color  of  bodies  heated  to  higher  and  higher  tem- 
peratures therefore  starts  with  red,  passing  thru  orange  and 
yellow,  tending  towards  white.  In  fact,  white  is  the  correct 
color  emitted  by  extremely  hot  bodies,  such  as  the  sun. 

The  estimations  of  temperature  from  measurements  of  lumi- 
nous radiations  may  be  made  directly  in  two  different  ways,  by 
utilizing 

First,  the  total  intensity  of  the  luminous  radiations; 

Second,  the  intensity  of  a  radiation  of  a  definite  wave  length. 

In  the  first  instance,  it  is  a  matter  of  common  experience  that 
the  brightness  of  substances  increases  very  rapidly  with  the 
temperature.  One  may  estimate  this  brightness  with  the  unaided 
eye,  but  this  method  is  very  uncertain  for  lack  of  a  constant  stand- 
ard of  comparison.  The  sensitivity  of  the  eye  varies  with  the 
individual,  with  the  light  which  the  eye  has  received  immediately 
before  the  observation,  and  with  the  attendant  fatigue.  Photo- 
metric instruments  constructed  for  the  measurement  of  total 
intensity,  while  precise  when  used  as  a  comparison  instrument 
continually  viewing  some  standard  source,  cannot  be  employed 
on  account  of  the  variation  in  the  distribution  thruout  the 
spectrum  of  the  radiant  energy  emitted  from  different  hot 
bodies,  which  results  in  the  fact  noted  above:  that  different 
bodies,  at  the  same  temperature,  appear  to  be  differently 
colored.  The  method  of  using  the  total  photometric  brightness 
as  a  measure  of  temperature,  therefore,  lacks  sensitiveness,  as 
well  as  definiteness,  and  is  better  replaced  by  methods  based  on 
the  use  of  a  single  wave  length. 

It  might  be  thought  that  the  same  objections  would  apply 
in  the  second  method  of  temperature  measurement,  that  is,  by 
estimating  the  intensity  of  a  radiation  of  definite  wave  length. 
However,  a  great  many  important  substances  have  an  emissive 
power  approaching  unity,  while  the  variation  of  radiation  with 
temperature  is  sufficiently  marked  so  that  the  errors  committed 
in  neglecting  the  emissive  power  are  small.  Thus,  the  emissive 
powers  of  nearly  all  bodies  at  high  temperatures  are  greater  than 
0.5.  By  assuming  this  factor  equal  to  0.75,  the  greatest  error 


RADIATION  AND   OPTICAL  PYROMETERS 


117 


possible  between  the  ordinary  temperatures  of  1000°  C.  and  1500° 
C.  will  be  from  25°  to  50°. 

An  optical  pyrometer  devised  upon  this  principle  has  been 
perfected  by  LeChatelier  (Fig.  18),  while  the  Shore  Pyroscope 
(Fig.  19)  uses  a  similar  principle,  except  that  the  parts  are 
arranged  in  a  slightly  different  manner. 

These  pieces  of  apparatus  consist  essentially  of  a  small  corn- 


Absorbing  Glass 


Objective 


Iris  I  S  Diaphragm 


FIG.  1 8. — Diagram  of  Le  Chatelier  Optical  Pyrometer. 

parison  lamp  attached  laterally  to  a  direct  vision  telescope. 
The  image  of  the  flame  of  this  lamp  is  projected  on  the  edge  of 
a  mirror  (M,  Fig.  18,  R,  Fig.  19)  placed  at  an  angle  of  45°, 
at  the  principal  focus  of  the  telescope.  In  using  the  instrument, 
one  equalizes  the  intensity  of  the  images  of  the  hot  body  and  of 
the  comparison  flame,  these  images  being  side  by  side.  This  is 
done  by  placing  variously  tinted  and  calibrated  glasses  before 
the  ocular  or  the  objective  of  the  telescope  viewing  the  hot  body, 
and  simultaneously  adjusting  the  opening  of  the  iris  diaphragm. 


118 


EXPERIMENTAL   GROUP  III 


The  temperature  is  then  computed  from  the  proper  formulas 
derived  during  the  calibration,  or  directly,  if  the  instrument  has 


Kerosene  Lamp 

R= Comparison  Reflector 


FIG.  19. — Sectional  Plan  of  Shore  Pyroscope. 

been  standardized  and  the  scale  attached  to  the  iris  diaphragm 
properly  marked  in  degrees  of  temperature. 


RADIATION  AND   OPTICAL  PYROMETERS 


119 


The  Wanner  pyrometer  (Fig.  20)  uses  as  a  comparison  lamp 
a  6- volt  incandescent  lamp,  illuminating  a  glass  matte  surface. 
Monochromatic  red  light  is  produced  from  both  the  standard 
lamp  and  the  observed  body  by  passing  their  radiations  thru 
a  direct- vision  spectroscope  and  screen  which  cuts  out  all  but  a 
narrow  band  in  the  red  end  of  the  spectrum.  The  photometric 
comparison  is  made  by  adjusting  both  halves  of  the  field  to 
equality  by  means  of  a  polarizing  arrangement,  which  consists 
of  a  complex  system  of  prisms  and  lenses.  The  eye  observes  a 
round  field,  the  upper  and  lower  parts  of  which  are  formed  by 
light  from  the  standard  lamp  and  the  hot  object  respectively. 


FIG.  20. — Wanner  Pyrometer  in  Standardizing  Frame. 

By  proper  rotation  of  a  pair  of  Nicol  prisms  these  two  fields  are 
adjusted  to  equal  intensity,  when  the  temperature  of  the  hot 
body  is  read  directly  from  an  attached  dial. 

The  accuracy  of  this  pyrometer  evidently  is  independent 
of  drafts  and  air  conditions  which  affect  the  lamps  of  the  Le- 
Chatelier  and  Shore  types,  but  does  depend  upon  the  constancy 
of  light  emitted  by  the  standard  incandescent  lamp.  This 
varies  with  age  to  a  slight  extent,  but  more  particularly  with  the 
momentary  variation  of  the  electromotive  force  of  the  battery. 
This  battery  should  evidently  be  one  of  large  capacity  and  of 
constant  potential.  It  is  therefore  necessary  frequently  to  check 
the  constancy  of  illumination  of  the  electric  lamp. 


120  EXPERIMENTAL   GROUP  III 

This  is  done  after  the  manner  shown  in  the  illustration, 
Fig.  20.  Set  the  dial  on  the  "  normal  point  "  and  view  a  stand- 
ard amyl-acetate  flame  under  standard  conditions.  If  the  two 
parts  of  the  field  are  not  exactly  of  the  same  intensity,  the  cur- 
rent passing  thru  the  filament  of  the  comparison  lamp  should 
be  adjusted  by  a  suitable  resistance  in  series.  A  delicate  ammeter 
in  circuit  should  also  be  read.  The  pyrometer  is  now  ready  for 
intermittent  operation  for  some  hours,  if  the  external  resistance 
in  the  battery  circuit  is  kept  in  such  adjustment  that  the  proper 
amount  of  current  is  flowing  thru  the  filament,  as  shown  by 
the  ammeter. 

Still  a  third  method  of  measuring  radiation  was  first  used  by 
Morse,  and  independently  developed  by  Holborn  and  Kurl- 
baum,  as  follows:  If  a  sufficient  current  is  sent  thru  a  fila- 
ment of  an  electric  lamp,  the  filament  glows  red  at  first,  and  as 
the  current  increases,  the  filament,  getting  hotter  and  hotter, 
becomes  orange,  yellow,  and  white,  just  as  any  progressively 
heated  body.  If  now  this  filament  is  interposed  between  the  eye 
and  an  incandescent  object,  the  current  thru  the  lamp  may 
be  adjusted  until  a  portion  of  the  filament  is  of  the  same  color 
and  brightness  of  the  object.  At  this  instant,  the  filament 
becomes  invisible  against  the  bright  background,  and  the 
current  then  becomes  a  measure  of  the  temperature.  An 
absolute  match  of  both  color  and  brightness  cannot  be 
made  unless  monochromatic  light  is  used,  which  is  effected  by 
proper  colored  glasses  built  into  the  ocular  of  the  observing 
telescope. 

The  telescope  (Fig.  21)  also  contains  a  special  incan- 
descent lamp  energized  by  a  small  lead  storage-battery.  This 
battery,  with  adjustable  resistance  and  a  very  sensitive  but 
rugged  ammeter,  are  compacted  into  a  small  case.  When 
in  use,  the  hot  body  whose  temperature  is  desired,  is  viewed 
thru  the  telescope,  and  the  proper  current  passed  thru 
the  lamp  filament  until  it  vanishes  against  the  background. 
The  current  now  flowing  deflects  the  needle  over  a  dial 
calibrated  to  read  degrees  of  temperature.  The  system  is 


RADIATION  AND   OPTICAL  PYROMETERS 


121 


very  rugged,  precise,  compact,   and  easily  operated  even  by 
novices. 

The  accuracy  depends  upon  the  condition  of  the  lamp  and 
filament,  which  changes  only  after  months  of  intermittent  use. 
The  storage  battery  needs  to  emit  a  constant  current  only  for  a 
sufficient  time  to  read  the  ammeter — which  latter,  of  course, 
must  be  of  high  grade.  Below  800°  C.  the  measurements  are 
more  easily  made  without  any  red  glass,  as  the  filament  itself 
is  then  red.  The  lowest  limit  of  this  instrument  is  about  600°  C. 
Two  red  glasses  are  required  above  1200°  C.,  and  a  mirror 


45  Mirror 
Absorbing  Screea 


Rheostat 


Shunt 
:&Iilli  Ammeter 


Section  on  A-C 

FIG.  21. — Diagrammatic  Representation  of  the  Wanner  Pyrometer. 

absorbing  screen  above  1600°  C.  All  of  these  combinations, 
of  course,  require  individual  calibration.  At  very  high  tem- 
peratures, the  pyrometry  becomes  difficult,  the  filament  never 
entirely  disappearing,  unless  strictly  monochromatic  glass  screens 
are  provided. 

Special  Apparatus.     The  special  apparatus  needed  is  as  fol- 
lows: 

Radiation  and  optical  pyrometers  of  various  kinds. 
Cracked  bodies,  such  as  steel  disks,  clay  crucibles,  refrac- 
tory bricks. 

Fused  quartz  tube,  closed  at  one  end. 
Electrical  meter. 


122  EXPERIMENTAL   GROUP  III 

Laboratory  Equipment.  The  laboratory  equipment  need  d 
is  as  follows: 

Hot  furnace  in  equilibrium. 

Procedure,  a.  Before  working  with  optical  or  radiation 
pyrometers,  obtain  a  demonstration  of  its  manipulation  from  the 
instructor.  Calibration  curves  of  the  various  instruments  should 
also  be  obtained. 

b.  The  work  will  be  to  observe  the  temperature  of  various 
furnaces  in  the  laboratory  at  intervals,  reporting  the  results  to 
the  captain  of  the  respective  squads. 

c.  Various  precautions  should  be  carefully  noted: 

Do  not  place  a  pyrometer  so  close  to  a  hct  body  that  it  may 
be  blistered,  warped,  or  otherwise  injured  by  the  radiating 
heat.  A  sufficiently  large  opening  or  portion  of  the  hot  body 
must  be  observed  to  fill  the  telescopic  field.  Interrupt  the  heat- 
ing current  between  observations. 

d.  Place  the  various  cracked  objects  in  a  muffle  equipped  with 
a  temperature  regulator,  and  bring  the  furnace  to  equilibrium 
at  about  1000°.     Also  insert  the  quartz  tube  thru  a  suitable 
hole  in  the  furnace  casing,  so  that  the  closed  end  will  be  within 
the  furnace  laboratory. 

e.  When  the  furnace  has  maintained  a  steady  temperature  for 
thirty  minutes,  observe  the  temperature  of  the  bottom  of  the 
quartz  tube  by  all  the  optical  pyrometers  furnished  you,  as  well 
as  the  calibrated  thermo-couple  in  possession  of  the  squad. 

/.  Remove  the  quartz  tube  and  observe  the  apparent  tem- 
perature of  the  furnace  atmosphere  thru  the  same  hole  by 
all  the  methods  of  procedure  e.  If  the  pyrometer  is  an  optical 
pyrometer,  obtain  the  temperature  by  taking  two  readings 
—the  first  approaching  equality  in  the  fields  from  below  and 
the  second  from  above  the  unknown  temperature.  Read  each 
determination  and  use  the  average  value  for  the  temperature  of 
the  furnace. 

g.  Open  the  furnace  door,  draw  one  of  the  enclosed  objects 


RADIATION  AND   OPTICAL  PYROMETERS  123 

quickly  forward  near  the  opening,  and  observe  its  temperature 
with  the  Morse  pyrometer.  First  observe  the  body  of  the  piece, 
and  second,  obtain  a  match  against  the  radiation  issuing  from 
the  crack.  This  must  be  done  quickly,  and  by  the  most  skil- 
ful member  of  the  squad.  Then  close  the  door  of  the  furnace 
for  several  minutes,  and  repeat  the  procedure  until  all  the 
objects  have  been  observed. 

Queries,  a.  If  the  intensity  of  the  heat  radiated  from  a  body 
at  1000°  C.  is  R,  what  will  be  the  intensity  at  1500°  C.?  At 
2000°  C.? 

b.  What  is  the  true  temperature  of  the  furnace  as  measured 
in  procedure  e  and  /?    Discuss  the  causes  for  any  variations 
noted. 

c.  Give  precautions  to  be  observed  in  obtaining  the  tempera- 
ture existing  in  the  melting  zone  of  a  cupola. 

e.  Give  precautions  to  be  observed  in  obtaining  the  tem- 
per^ture  of  a  tilting  furnace  melting  copper-bearing  metals,  which 
tinge  the  flame  various  shades  of  green. 

/.  Figure  the  emissivity  of  the  substances  observed  in  pro- 
cedure g. 

h.  Discuss  the  advantage  of  optical  pyrometry  over  the  use 
of  the  thermoelectric  principle. 


EXPERIMENTAL  GROUP  IV 
FOREWORD  TO  THE  STUDENT 

This  group  comprises  a  series  of  experiments  on  steels. 
Starting  with  No.  16,  which  obtains  the  thermal  equilibria  for 
low  percentage  carbon  alloys — that  is  to  say,  for  steels — the  fol- 
lowing series  of  four  experiments  develops  the  application  of 
this  equilibrium  diagram  to  such  important  matters  as  grain 
size,  hardening,  tempering,  toughening,  and  annealing. 

These  various  matters,  properly  understood,  should  enable  the 
student  to  make  a  rugged  metal-  or  wood-cutting  tool  of  simple 
shape,  which  is  the  subject  of  Experiment  No.  21. 

Experiment  No.  22  studies  the  relation  between  microscopic 
structure  and  the  physical  properties  developed  in  Experiments 
Nos.  17  to  20,  inclusive.  Short  courses  may  possibly  find  no 
time  for  this  experiment,  altho  procedures  a  to  f  inclusive 
can  be  performed  in  one  afternoon,  and  will  give  the  student  a 
view  of  all  the  various  constituents  of  hardened  and  tempered 
steel.  More  extensive  courses  can  include  procedures  g  to  h, 
while  i  andy  will  be  performed  by  students  specializing  in  metal- 
lography. 

Experiment  No.  23  is  designed  to  give  the  student  an  intelli- 
gent appreciation  of  the  subject  of  case-hardening,  or  more 
properly,  "  case-carburizing."  Experiment  No.  24  is  an  intro- 
duction to  the  baffling,  but  none  the  less  insistent,  problems 
presented  by  the  corrosion  of  iron  and  steel. 


124 


EXPERIMENT  NO.  16 
TRANSFORMATION  POINTS 

Object.  The  object  of  this  experiment  is  to  show  that  iron 
has  abrupt  changes  in  its  physical  state  at  temperatures  below 
the  melting-point. 

General  Explanation.  In  Experiment  No.  8  it  was  shown  that 
when  a  continuous  cooling  curve  is  produced,  all  the  heat  is 
radiating  at  the  expense  of  the  sensible  heat  of  the  body.  On  the 
other  hand,  a  discontinuity  denotes  that  some  part  of  the  heat 
transfer  is  due  to  latent  heat,  involving  internal  change  in  the 
alloy  itself.  It  is  easy  to  comprehend  that  the  large  latent  heats 
of  fusion  or  vaporization  (which  are  absorbed  when  a  solid 
changes  into  a  liquid,  or  a  liquid  into  a  gas,  respectively),  will 
profoundly  change  the  shape  of  a  heating  curve.  However, 
there  are  other  changes  indicated  by  the  thermal  analysis  of  many 
alloys  which  occur  after  the  body  has  become  entirely  solidified. 
These  so-called  transformation  points  or  ranges  may  be  caused 
by  chemical  reactions  taking  place  within  the  solid,  substances 
being  precipitated  from  a  "  solid  solution,"  or  a  sudden  change  in 
some  physical  property  of  the  components,  such  as  in  magnetism, 
hardness,  or  specific  gravity. 

It  may  be  difficult  to  comprehend  that  such  changes  can 
occur  in  a  body  after  it  has  become  entirely  solidified,  owing 
to  the  usual  conception  that  the  particles  are  then  rigidly  fixed. 
However,  this  rigidity  is  only  comparative.  The  molecules 
in  the  solid  state  have  not  the  large  mobility  they  possess  as  a 
liquid,  but  even  so,  they  are  still  moving  in  circumscribed 
orbits,  and  have  the  power,  under  proper  conditions,  to  rearrange 
their  position  or  internal  configuration.  In  general,  such  re- 
arrangement is  accompanied  by  a  sudden  change  in  some  physical 

125 


126  EXPERIMENTAL  GROUP  IV 

property  and  in  the  total  energy  of  the  molecule,  which  latter  is 
evidenced  by  a  spontaneous  evolution  or  absorption  of  latent 
heat.  The  freedom  of  molecular  movement  depends  upon  the 
temperature,  being  greatest  at  elevated  temperatures,  becoming 
less  with  cooling  until  absolute  zero  is  reached,  where  all  mole- 
cular and  intra-molecular  motion  ceases.  Molecular  changes 
in  the  solid  occur  thru  a  temperature  range,  rather  than  being 
well  defined  at  a  certain  degree. 

Cooling  curves  of  the  purest  iron  show  at  least  two  well- 
defined  discontinuities  at  temperatures  more  than  600°  C. 
below  its  freezing-point.  It  seems  that  the  soft,  magnetic  metal 
so  familiar  as  wrought  iron,  and  called  "  alpha  iron  "  or  "  f er- 
rite  "  by  the  metallurgist,  becomes  unstable  at  about  760°  C., 
and  changes  into  the  so-called  "  beta  "  modification,  becoming 
suddenly  harder,  and  losing  its  magnetism.  This  state  in  turn 
persists  no  higher  than  930°  C.,  when  a  softer,  non-magnetic 
u  gamma  "  iron  is  the  stable  modification  up  to  the  actual  melt- 
ing-point of  the  metal.  These  various  changes  occur  in  elec- 
trolytic iron,  and  therefore  cannot  be  attributed  to  any  chemical 
reaction  or  solution;  they  are  entirely  due  to  the  existence  of 
"  allo tropic  modifications  "  of  the  iron  in  its  solid  state.  Such 
modifications  are  by  no  means  rare — sulfur  possesses  the  various 
forms  typified  by  rhombic  crystals,  stable  up  to  96°  C.;  mono- 
clinic  crystals,  stable  between  96°  C.  and  the  melting-point, 
119°  C.;  a  pale-yellow,  mobile  liquid  called  gamma  sulfur, 
stable  between  the  melting-point  and  260°  C.;  a  dark,  viscous 
liquid,  stable  above  260°  C.,  called  mu  sulfur;  and  finally  a 
supercooled  form  of  mu  sulfur,  ordinarily  called  amorphous 
sulfur. 

Steels  (or  iron  containing  a  certain  amount  of  carbon)  develop 
somewhat  different  cooling  curves  from  those  produced  by  pure 
iron.  Thermal  examination  of  a  series  of  these  iron-carbon 
alloys  will  form  an  equilibrium  diagram  in  the  solid  similar  to 
that  which  the  water-salt  system  developed  in  the  liquid  (as 
discussed  in  detail  in  Experiment  No.  10),  namely,  the  under- 
lined V:  CY).  The  lines  and  areas  of  the  two  diagrams  have  an 


TRANSFORMATION  POINTS  127 

entirely  parallel  significance,  and  for  this  and  otner  sufficient  rea- 
sons it  is  thought  that  at  high  temperatures  the  various  constitu- 
ents of  steels  are  in  a  "  solid  solution."  The  decomposition  of 
the  solid  solution  occurs  in  a  similar  manner  to  the  decomposition 
of  the  liquid  solutions  already  studied.  In  passing,  it  should  be 
noted  that  the  carbon  really  does  not  exist  in  the  alloy  as  free 
carbon,  but  combines  with  iron  to  form  an  iron  carbide,  FeaC, 
which  is  called  cementite.  Therefore  the  diagram  is  really  one 
between  ferrite  and  cementite,  rather  than  between  iron  ai*d 
carbon.  It  should  also  be  noted  that  the  word  "  eutectoid  " 
is  used  instead  of  the  word  "  eutectic  "  to  denote  the  solidified 
and  separated  mother  liquor  of  a  solid  solution.  This  termi- 
nology is  used  to  distinguish  it  from  the  analogous  material  solid- 
ified from  a  liquid  mother  liquor,  to  which  the  term  eutectic  is 
more  properly  restricted. 

A  detailed  explanation  of  the  phenomena  attending  the  slow 
heating  and  cooling  of  iron-carbon  alloys  is  given  in  Mills, 
"  Materials  of  Construction,"  pp.  423  to  429  inclusive,  which  the 
student  should  review  in  this  connection. 

Special  Apparatus.  The  special  apparatus  needed  is  as  fol- 
lows: 

Electric  pot  furnace  of  Experiment  No.  14. 

One  rheostat,  0-20  ohms. 

One  ammeter,  o-io  amperes. 

One  voltmeter,  o-i  10  volts. 

One  polarity  socket. 

One  millivoltmeter  or  potentiometer. 

Six  pieces  of  rubber-covered  flexible  lead  wire. 

Supplies.     The  supplies  needed  are  as  follows: 

Ice. 

Three  feet  of  soft  iron  wire. 

Fourteen  rods  of  steel,  f  in.  diameter,  6  in.  long,  with 
carbon  content  stamped  upon  each  piece. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 


128  EXPERIMENTAL  GROUP  IV 

Sack  of  kieselguhr. 

More  sensitive  pyrometric  equipment  for  squads  working 

on  lowest  carbon  steels. 
Large-scale  coordinate  paper  mounted  on  bulletin-board 

and  a  supply  of  pins  with  colored  heads. 

Procedure.  NOTE:  In  this  and  the  following  four  experi- 
ments it  is  desirable  to  provide  a  supply  of  plain  carbon  steels 
ranging  from  mild  to  high  carbon  tool  steel,  in  such  a  manner 
that  each  squad  may  work  with  a  separate  analysis.  The  experi- 
mental results  should  be  posted  on  proper  bulletin  boards  so 
that  at  the  end  of  the  experiment  complete  information  will  be 
available  to  all  students  showing  the  effect  of  increasing  carbon 
on  the  various  properties  under  investigation.  The  best  squads 
should  be  assigned  the  more  difficult  low  carbon  steels,  and  pref- 
erably provided  with  more  precise,  calibrated,  pyrometric 
equipment. 

a.  The  arrangement  for  taking  the  cooling  curve  of  steel 
varies  somewhat  as  to  the  shape  of  the  material  under  study. 
Thus,  a  bundle  of  thin  rods  may  be  wired  together,  with  the 
hot  junction  of  a  thermo-couple  at  the  geometric  center.     If  a 
larger  rod  or  block  is  used,  it  may  have  a  small  hole  drilled  into  its 
center,  and  the  hot  junction  inserted  therein;   or  two  flat  disks 
may  have  a  groove  filed  or  forged  on  their  surfaces,  then  wired 
tightly  together  with  the  bare  junction  between. 

b.  Take  the  thermo-couple  calibrated  in  Experiment  No.  9, 
and  strip  the  insulation  from  the  end  backward  for  a  distance  of 
one  inch.     Arrange  the  test  pieces  as  in  procedure  a,  and  place 
in  the  electric  wire-wound  pot  furnace,  leading  the  elements  out 
through  the  hole  in  the  lid,  thru  the  cold  end  ice  pail  to  the 
electrical  meter. 

c.  Connect  the  pot  furnace  to  a  polarity  socket,  as  shown 
in  the  wiring  diagram,  Fig.  15,  p.  109. 

d.  Raise  the  temperature  to  550°  C.  as  rapidly  as  consistent 
and  from  550°  C.  to  950°  C.  at  a  rate  of  about  10°  per  minute. 
Observe  and  plot  an  inverse  rate  curve  during  the  latter  interval 


TRANSFORMATION   POINTS 


129 


according  to  the  procedure  /  of  Experiment  No.  10,  noting  time 
for  each   quarter-unit.     Print  on   the  cross-section  paper   the 


Millivoltmeter  Readings  —  > 
%  %  8  K  S  § 

Data 
Temperature    Time    Interval 
37                  11:36.35        Knc 
36.5  M.V.      11:37:25            t>ec' 
36                   11:38:05 
35.5                11:38:55        TT 
35                    11:39:40 
34.5                11:40:30        iJjJj 

33.5                11:42:10        ?*' 
33                   11:42:55        f, 
32.5                11:43:50        ?T 
32                   11:44:45        « 
31.5                11:45-^0      ,^ 
31                   11:47:30      ,XX 
30.5                11:49:10      *5 
30                   11:50:25         '" 
20.5                11:51^0 
29                    11:53:11         ?} 
23.5                11:57:15       ™ 
28                   11  :58  :05        ?~ 
27.5                11:59.00        £? 
27                   11:59:45       ™ 
26.5                12:01K)0        '.? 
26                   12:01:45 

0 

0 

•       0 

0 

. 

A»M- 

32.6  M 

V.  =7 

75°C. 

\ 

^ 

x< 

0 

/ 

*  X 

- 

_ 

- 

M.V.  • 

•"' 

—  —  — 

=  695°( 

. 
—  i             — 

• 

•             •** 

»  i            • 

— 

:=- 

•0 

.f 

. 

0 

Fig.  22 

INVERSE  RATE 
COOUNG  CURVE 
OF 
0.38-C.  STEEL 

I 

s 

quad 

t 

50                      100                     150                      200                     250 
Time  Intervals  >- 

FIG.  22. — Inverse  Rate  Cooling  Curve  of  0.38  C,  Steel. 

temperature  corresponding  to  the  beginning  of  undoubted  dis- 
continuities in  the  rate  of  heat  absorption.  Be  careful  not  to 
exceed  a  temperature  of  1000°  C.,  on  account  of  the  danger  of 


130  EXPERIMENTAL   GROUP  IV 

burning  out  the  heating  element  of  the  furnace.  Do  not  change 
the  external  resistance  during  the  interval  550°  C.  to  950°  C. 

e.  Shut  off  the  current,  and  read  and  plot  as  in  Fig.  22  a 
similar  inverse  rate  cooling  curve  thru  the  same  range.  Hold 
the  temperature  at  550°  C.  while  the  curves  are  discussed  with 
the  instructor. 

/.  Repeat  procedure  d  and  e  at  a  considerably  slower  rate, 
regulating  the  speed  so  as  to  occupy  the  remainder  of  the  labora- 
tory period.  Place  additional  kieselguhr  over  the  lid  to  decrease 
the  cooling  speed. 

g.  Present  all  results  to  the  instructor,  and  stick  properly 
colored  pins  into  the  coordinate  diagram  on  the  laboratory 
wall,  locating  both  the  Ac  and  the  AT  transformations  determined 
by  your  curves. 

Queries,  a.  Construct  a  neat  equilibrium  diagram  showing 
the  decomposition  of  austenite,  after  the  style  of  Fig,  9,  page  74. 
Arrange  the  scale  so  that  the  carbon  content  will  range  up  to 
2  per  cent,  and  the  temperatures  between  500°  C.  and  1000°  C. 
Locate  the  Ac  points  determined  by  the  various  squads  with 
small  red  circles,  and  connect  by  a  red  line.  Locate  the  Ar 
points  and  lines  similarly  in  blue.  Also  draw  in  a  heavy  black 
line  the  equilibrium  diagram  (Ae  lines)  of  Fig.  23,  which  was 
adopted  by  Howe,*  after  weighing  the  best  information  now 
available  on  the  subject.  This  will  produce  a  sheet  of  cross- 
section  paper  showing  three  superimposed  diagrams  in  color 
— two  as  determined  in  our  laboratory,  the  third  represent- 
ing the  standard  adopted  by  Howe.  Label  all  lines,  coor- 
dinates and  areas. 

b.  Draw  the  heating  and  cooling  curves  derived  with  India 
ink.  Discuss  the  reasons  for  the  non-concurrence  of  the  corre- 
sponding A0  and  AT  points.  Has  this  lag  any  relation  to  the 
"  surfusion  "  shown  in  the  solidification  of  antimony?  What 
effect  should  time  have  upon  the  magnitude  of  this  hysteresis? 


*  See  Howe,  "  Metallography  of  Steel  and  Cast  Iron,"  page  130.  The  points 
located  on  the  diagram  are  from  cooling  curves  made  by  Carpenter  and  Keeling, 
I,  1904,  "  Journal  of  the  Iron  and  Steel  Institute,"  224. 


TRANSFORMATION  POINTS 


131 


Fig.  23 
HOWE'S  DIAGRAM 

/ 

V 

1500 

\ 

v^ 

Points  from 
Carpenter  and  Keeling 

/ 

V 

;• 

°o( 

X 

x 

/ 

^400 

\ 

0 

> 

\ 

y 

i 

0 

X 

\ 

/ 

\ 

x 

x 

Tamperature  i  Degrees  Centigrade  —  > 

\ 

\ 

0 

N 

x 

1 

\ 

\ 

X 

\ 

1 

\ 

X 

- 

\ 

x 

/ 

•^, 

j 

0 

\j 

0 

/ 

D 

1 

/ 

0  ( 

0 

7 

0 

0 

/ 

0 

/ 

0 

\ 

/ 

0 

"° 

\ 

/ 

\ 

0 

0 

o 

0 

0 

0 

o    V 

s 

\ 

—0 

0 

0  0 

0 

0 

°o 

0 

0 

0° 

; 

0 

0 

0 

0 

0 

0 

*LO                      2.0                     3.0                      4.0                     5.0 

Per  cent  Carbon — &- 
FIG.  23. — Howe's  Diagram. 


132  EXPERIMENTAL  GROUP  IV 

c.  In  the  light  of  the  above  general  explanation,  and  also  of 
your  study  of  the  lead-antimony  diagram,  explain  the  actions 
proceeding  in  the  metal  at  all  times  during  the  heating  and 
cooling. 

d.  Define   allotropy.     Give   the   allotropic  modifications   of 
some  other  substances  than  iron  and  sulfur.     Give  an  explana- 
tion of  allotropy  based  upon  the  molecular  theory,  as  suggested 
by  the  allotropy  of  oxygen. 


EXPERIMENT  NO.  17 
CRYSTALLIZATION  OF  STEEL 

Object.  The  object  of  this  experiment  is  to  show  the  growth 
and  restoration  of  the  crystalline  grain  in  a  piece  of  steel  thru 
various  heat  treatments. 

General  Explanation.*  Before  the  analytical  chemist  came 
into  the  steel  plant, — not  so  many  years  ago, — eye  examination 
of  a  bright  fracture  was  the  only  method  at  the  disposal  of 
iron  makers  for  classifying  their  product.  Indeed,  at  the  present 
day,  the  skilled  melters  operating  a  modern  open-hearth  steel 
furnace,  cast,  break,  and  examine  the  fracture  of  small  pigs  of 
metal  at  definite  intervals  of  time,  in  this  way  gaining  accurate 
information  as  to  the  elimination  of  the  impurities  in  the  bath, 
and,  toward  the  finish,  predicting  the  carbon  content  of  the  steel 
to  within  a  few  points.  Pig  iron  is  commonly  sold  by  the  appear- 
ance of  the  fracture,  which,  by  the  way,  is  the  universal  reliance 
of  the  "  practical "  foundryman.  The  fracture  of  "  spies " 
withdrawn  from  cementation  boxes  indicates  the  progress  of  the 
carburization  (v.  "  Mills,  Materials  of  Construction,"  page  364), 
and  each  cemented  bar  is  broken,  examined,  and  classified  as 
to  carbon  content  before  being  melted  into  crucible  steel.  Test 
lugs  from  case-carburizing  and  malleableizing  boxes  (op.  cit.  pp. 
421,  336)  are  regularly  broken  to  indicate  quickly  the  quality 
of  the  product. 

In  this  way  the  skilled  operator  is  enabled  to  determine  the 
homogeneity  and  approximate  chemical  composition  of  an 
iron-carbon  alloy,  if  the  previous  heat  treatment  is  known.  On 
the  other  hand,  a  skilled  inspector  can  approximately  determine 

*  A  detailed  discussion  of  the  points  covered  by  this  experiment  may  be  had 
in  Stoughton,  "  Metallurgy  of  Iron  and  Steel,"  pp.  357-368. 

133 


134  EXPERIMENTAL  GROUP  IV 

its  past  heat  treatment,  and  probable  strength  and  brittleness  by 
the  fracture,  if  the  carbon  content  of  a  steel  is  known.  Pro- 
gressive manufacturers  are  controlling,  supplementing,  and 
checking  their  fracture  indications  by  chemical  analyses,  while 
wide-awake  engineers  are  demanding  more  thorogoing  frac- 
ture tests,  supplemented  by  metallographical  analysis,  to  con- 
trol their  acceptances.  At  the  present  time,  railway  engi- 
neers are  demanding  that  top  rails  from  each  ingot  be  tested 
under  the  drop-hammer  (see  Fig.  24),  while  rail  manufacturers 
are  insisting  that  the  present  practice  of  testing  random  rails 


FIG.  24. — Undesirable  Rails. 

Reproduced  from  "  The  Engineering  News-Record,"  by  permission  of  the  McGraw-Hill 

Publishing  Co. 

from  each  heat  is  sufficient.  Bridge  and  mechanical  engineers 
are  coming  to  the  conclusion  than  many  disastrous  failures 
attributed  to  "  crystallization  under  alternating  stresses  "  are 
in  reality  due  to  the  brittleness  induced  by  the  coarse  crys- 
tallization resulting  from  improper  heat  treatment  during 
fabrication,  and  are  relying  upon  their  inspectors  to  reject  such 
pieces  at  the  steel  mills. 

Microscopic  examination  has  confirmed  the  supposition  that 
a  piece  of  metal  is  essentially  an  aggregate  of  small  crystalline 
grains  cemented  together  with  a  thin  film  of  non-crystalline  (or 
amorphous)  material.  (See  Experiment  No.  n).  It  seems 
that  the  amorphous  cement  is  stronger  and  tougher  than  the 
crystalline  aggregate;  therefore,  when  a  piece  of  such  material 


CRYSTALLIZATION  OF  STEEL  135 

fails,  the  fracture  passes  thru  the  crystals  themselves,  along 
well-defined  cleavage  or  parting  planes,  rather  than  around  the 
rougher  superficies  of  the  individual  crystals.  Consequently, 
the  fresh  fracture  will  show  bright  flashes  of  light  reflected  from 
the  small,  flat,  parting  planes.  The  larger  the  crystalline  grain, 
the  larger  the  parting  planes,  and  the  coarser  and  more  fiery  the 
fracture.  The  finer  the  crystals,  the  greater  the  percentage  of 
amorphous  material,  the  stronger  and  tougher  the  steel,  and  the 
more  silky  the  fracture. 

If  cast  steel  (Fig.  25)  is  held  at  a  high  temperature,  the  crys- 
talline grain  does  not  seem  to  grow  coarser.  Once  the  crystals 
of  this  casting  have  been  broken  up  and  intermixed  by  hammer- 
ing, rolling,  or  other  mechanical  kneading  (Fig.  27),  the  grain 
size  is  strictly  dependent  upon  the  heat  treatment  subsequently 
imparted  to  the  bar.  (Fig.  28).  It  seems  that  even  a  moderate 
degree  of  heat  (500°  C.),  if  continuously  applied,  is  sufficient  to 
cause  growth  in  the  grain  size,  ultimately  inducing  weakness 
and  failure  thru  a  phenomenon  called  "  Stead's  brittleness." 
Furnace  buckstays,  crane  chains,  and  other  members  repeatedly 
heated  to  such  temperatures  should,  therefore,  be  annealed  at 
intervals  to  restore  their  original  properties. 

A  very  short  time  at  an  extreme  temperature  will  cause  the 
same  grain  growth,  and  the  finest  steel  can  be  absolutely  ruined 
by  long  exposure  at  high  temperature  if  followed  by  no  subse- 
quent working  or  heat  treatment.  In  welding  and  forging 
practice,  the  blacksmith  guards  against  this  danger  by.  contin- 
ually hammering  the  metal  until  it  has  cooled  to  a  red  heat,  less 
than  900°  C.,  in  order  constantly  to  break  up  the  growing  crys- 
tals. Below  Arz,  mechanical  work  is  abandoned,  because  the 
rate  of  growth  is  then  quite  slow,  and  the  metal  has  lost  the 
plasticity  which  is  required  for  hot  working. 

Fortunately,  unless  the  steel  has  been  absolutely  ruined  by 
overheating  to  the  point  of  incipient  fusion,  and  therefore 
"  burned  "  (Fig.  29),  all  previous  crystalline  structure  seems  to 
be  obliterated  by  a  reheating  thru  Ac\,  at  which  transforma- 
tion range  a  new  and  independent  accumulation  of  crystalline 


FIG.  25. — Cast  Ingot.  FIG.  26. — Forged  and  Reheated  Nearly  to  Acz. 


FIG.  27. — Reheated  Considerably 
above  Ac$. 


FIG.  28. — Reheated  Much 
above  Ac3. 


FIG.  29. — Reheated  Past  Burning  Point. 

(Photomicrographs  by  E.  P.  Stenger,  of  0.35  Carbon  Steel.     All  at  75  diam.) 

136 


CRYSTALLIZATION  OF  STEEL  137 

nucleii  seem  to  come  into  existence.  Growth  of  these  new 
crystals  begins  at  this  range,  and  continues  with  increasing  rate 
at  higher  temperatures.  Annealing  for  restoring  the  grain,  and 
for  inducing  the  maximum  toughness  possible  for  a  given  carbon 
content,  should  therefore  be  carried  no  higher  than  to  make 
sure  that  the  whole  mass  of  the  steel  has  definitely  passed  Aci. 
However,  a  certain  qualification  is  necessary  for  low-carbon 
steels,  as  follows:  the  primary  ferrite  crystals  are  not  entirely 
absorbed  into  the  solid  solution  until  Ac%  has  been  passed,  nor 
are  all  traces  of  the  old  structure  entirely  eliminated  until 
enough  time  has  been  given  above  Acs  for  a  thoro  diffusion 
of  the  iron  molecules  into  the  surrounding  austenite.  (Fig.  26.) 
During  this  time,  however,  the  new  crystalline  orientation  is 
growing  apace;  one  is,  therefore,  between  the  horns  of  a  dilemma, 
but  it  will  generally  be  found  that  for  hypo-eutectoid  steels  a 
thoro  mechanical  working  (producing  a  very  small  uniform 
grain),  followed  by  annealing  slightly  above  Acs,  will  give  the 
best  physical  properties  to  the  piece. 

Special  Apparatus.     The   special  apparatus  required  is  as 
follows : 

One  electrical  meter. 
Supplies.     The  supplies  needed  are  as  follows: 

One  piece  |-in.  wrought-iron  gas  pipe,   12  in.  long  with 

closed  end. 
Four  bars  from  Experiment  No.  16,  two  of  which  will  be 

further  useful. 
Box  of  gummed  labels. 

Laboratory  Equipment.    The  laboratory  equipment  needed 
is  as  follows: 

Ice. 

Crucible  furnace,  at  1250°  C. 

Set  of  alphabet  punches. 

Anvil. 

Three-pound  blacksmith's  hammer. 


138  EXPERIMENTAL  GROUP  IV 

Scleroscope. 

Emery  wheel. 

Impact  machine. 

Optical  pyrometer. 

Five-gallon  water  pail  for  quenching  bath. 

Vises. 

Procedure.  NOTE.  High-carbon  steels  are  best  to  show  crys- 
talline growth  at  high  temperatures.  Medium  carbon  steels 
can  also  be  used.  Lower  carbon  steels  should  be  nicked  deeper, 
but  even  so,  some  will  not  break  without  large  bending,  which 
spoils  the  appearance  of  the  fracture.  These  steels  should, 
therefore,  be  sawed  off,  and  studied  microscopically  by  the  better 
squads,  and  a  series  of  specimens  mounted,  at  equal  magnifica- 
tions, for  inspection  by  the  whole  class. 

a.  Saw  about  three-eighths  of  the  way  thru  two  of  the 
rods  of  Experiment  No.  15  at  f-in.  intervals.  Mark  the  sec- 
tions consecutively  with  alphabetical  punches.  Put  one  of  these 
nicked  bars,  together  with  another  of  the  plain  bars  from  Experi- 
ment No.  1 6,  in  the  hot  crucible  furnace.  Delegate  one  mem- 
ber of  the  squad  to  hold  this  furnace  as  close  to  1250°  C.  as  pos- 
sible, maintaining  a  reducing  flame  at  all  times.  Allow  the 
notched  piece  to  remain  in  the  furnace  thirty  minutes  and  then 
remove  it  and  allow  it  to  cool  in  the  air.  The  plain  bar  is  to 
remain  in  the  hot  crucible  two  hours,  cooled  in  air,  and  then  used 
in  procedure/. 

.  b.  Break  one  section  from  the  ends  of  both  notched  bars  by 
placing  them  in  the  round  hole  in  the  anvil  and  striking  a  sharp 
blow  with  a  3-lb.  hammer.  Vises  must  not  be  used  for  breaking 
specimens.  Examine  the  fractures,  and  save  the  small  pieces 
for  further  comparison.  Paste  a  small  gummed  label  around 
each  fragment,  giving  its  carbon  content  and  heat  treatment. 

c.  Place  the  two  notched  pieces  alongside  each  other  in  the 
oven  furnace  and  heat  (anneal)  successively  to  the  following 
temperatures:  Aci  —  $o0-,  ^1  +  25°;  Ac3-2$°;  ^3  +  25°;  and 
then  by  100°  intervals  to  the  limit  of  the  furnace.  Measure  the 


CRYSTALLIZATION  OF  STEEL  139 

temperature  as  in  procedure  d.  After  each  temperature  has 
been  reached,  remove  the  bars  from  the  furnace,  cool  in  air, 
break  off  a  section,  examine,  and  label  as  before  noted. 

d.  Measure  the  temperatures  as  follows:    Place  your  cali- 
brated  thermo-couple,   properly  covered  with  asbestos  string 
(Experiment  No.  7)  in  a  i2-in.  protection  tube  of  f-in.  wrought- 
iron  pipe.     Insert  this  tube  thru  a  suitable  hole  in  the  side  or 
back  of  the  furnace  in  such  a  manner  that  the  hot  end  will  be 
directly  above  the  notched  bars.     A  reducing  flame  should  be 
maintained  at  all  times.    Adjust  the  couple  and  bars  correctly, 
close  the  door,  and  raise  the  temperature  very  gradually  up  to 
the  first  annealing  temperature  noted,  taking  at  least  fifteen  min- 
utes to  attain  that  degree,  and  making  sure  that  the  bars  and 
furnace  do  not  pass  that  heat.     The  door  of  the  furnace  may  be 
left  open  to  cool  the  muffle  slightly,  so  that  another  fifteen  min- 
utes will  be  consumed  in  heating  to  the  next  temperature,  and 
so  on.     Remove  the  thermo-couple,  and  use  an  optical  pyrometer 
for  temperatures  above  1000°  C. 

e.  Remove  only  one  bar  from  the  muffle  at  the  highest  tem- 
perature, and  try  to  refine  the  grain  of  the  other  by  allowing 
it  to  cool  in  the  furnace  to  just  above  Ac%,  and  then  quickly 
quench  by  plunging  it  endwise  into  a  pail  of  tap  water.    Dry 
the  bar  and  inspect  the  grain  size  by  breaking,  as  in  procedure  b. 

f.  Take  one  of  the  rods  of  Experiment  No.  16  and  anneal  it 
carefully  up  to  the  temperature  which,  according  to  your  experi- 
mental results,  produces  the  finest  grain.    Allow  it  to  cool  in  air 
from  that  temperature.     Both  this  bar,  and  the  bar  overheated 
for  two  hours  in  procedure  a  should  be  tested  for  relative  tough- 
ness in  the  impact  machine,  as  follows:   Mount  the  bars  in  the 
vise  so  that  about  one  inch  will  protrude,  and  strike  this  pro- 
jecting end  successive  blows  with  the  drop-hammer,  starting  at 
i-in.  fall,  then  2-in.,  then  3-in.  and  so  on  until  failure  ensues. 

g.  Grind  one  end  of  each  piece  flat,  and  test  the  hardness  with 
the  scleroscope. 

Queries,  a.  Take  a  piece  of  heavy  cardboard,  8|  in.Xn  in., 
letter  it  with  the  squad  number,  personnel  and  composition  of 


140  EXPERIMENTAL   GROUP  IV 

the  steel  treated.  Mount  all  the  steel  fragments  in  an  orderly 
manner  by  thrusting  them  thru  small  holes  cut  in  the  paste- 
board. Under  each  specimen  place  its  heat  treatment,  its  hard- 
ness, and  its  toughness,  if  determined  on  the  impact  machine. 
Place  this  sheet  on  the  bulletin  board  for  inspection  of  the  other 
squads. 

b.  Make  up  an  equilibrium  diagram  for  steel  on  coordinate 
paper  in  light  black  lines,  following  Fig.  23,  page  131.     Plot  upon 
this  diagram  the  hardness  numeral  of  all  the  fragments   tested 
by  the  laboratory  squads  as  posted  on  the  bulletin  board.     Draw 
contour  lines  of  equal  hardness  in  red. 

c.  By  examination  of  the  work  of  the  various  squads,  place 
a  heavy  black  line  on  this  diagram  showing  the  annealing  temper- 
ature which  produces  the  finest  grain. 

d.  What  effect  does  time  have  upon  the  grain  size;  if  the  tem- 
perature is  above  Acs?  below  Ac\? 

e.  Distinguish    between    overheated    and    "  burnt "    steel. 
Can  the  latter  be  again  restored  to  its  normal  condition  by  a 
heat  treatment? 

/.  Judging  from  the  experimental  data,  will  there  be  any 
change  in  the  grain  size  during  tempering? 

g.  Is  there  a  relation"  shown  between  grain  size  and  the  hard- 
ness and  ductility  of  steel?  Cite  figures. 

h.  How  would  one  measure  the  size  of  the  crystalline  grain? 

i.  Give  experimental  support  to  the  statement  on  page  125 
that  molecular  rearrangement  is  not  only  possible  in  the  solid 
state  but  molecular  migration  actually  covers  considerable  dis- 
tances. 


EXPERIMENT  NO  18 
HARDENING  OF  STEEL 

Object.  The  object  of  this  experiment  is  to  study  the 
hardness  of  steel  as  affected  by  quenching  temperature  and 
carbon  content. 

General  Explanation.  It  has  been  known  since  prehistoric 
times  that  certain  irons,  if  quickly  cooled  from  a  bright  red  heat 
became  very  hard  indeed,  and  could  then  be  formed  into  most 
useful  and  durable  cutting  tools.  This  discovery  marked  the 
last  milestone  of  the  evolution  of  man,  and  foreshadowed  modern 
civilization. 

The  curious  phenomena  of  hardening  are  yet  controlled  by 
rule  of  thumb  methods  which  are  closely  guarded  trade  secrets. 
During  the  last  century,  the  advent  of  chemical  analysis  indicated 
a  close  correspondence  between  the  hardening  power  of  irons  and 
their  carbon  content;  thus,  wrought  iron  containing  practically 
no  carbon  could  not  be  usefully  hardened,  while  steels  containing 
an  increasing  amount  of  carbon  were  capable  of  taking  a  harder 
and  harder  edge.  The  exact  cause  of  hardening  is  still  an 
unsolved  mystery,  despite  the  enormous  amount  of  scientific 
research  which  has  been  expended  upon  the  problem  in  the  last 
twenty  years,  even  applying,  as  it  has,  the  utmost  resources  of 
such  powerful  investigative  weapons  as  physical  chemistry  and 
metallography.  Several  hypotheses  are  under  discussion  as 
among  the  possibilities,  each  of  which  has  its  ardent  supporters; 
and  for  the  most  recent  exposition  of  our  knowledge  on  this 
matter  the  student  is  referred  to  Howe,  "  The  Metallography 
of  Steel  and  Cast  Iron,"  pages  173  to  196. 

From  the  point  of  view  of  practice,  the  hardening  operation 
consists  of  two  parts;  first,  heating  the  metal  uniformly  to  the 

141 


142  EXPERIMENTAL  GROUP  IV 

proper  temperature,  and  second,  cooling  it  quickly  and  uniformly. 
The  first  operation  presupposes  a  well-designed  furnace,  uniform 
in  temperature  from  top  to  bottom  and  end  to  end,  operating 
steadily  with  a  neutral  flame  ("  hazy  heat  ")•  Modern  produc- 
tion of  quantity  work  demands  a  heat  control  more  delicate  than 
the  unaided  eye,  and  pyrometers  are  installed  in  all  furnaces 
where  quality  and  uniformity  are  prerequisite. 

The  metal  must  be  in  the  furnace  long  enough  to  attain  the 
furnace  temperature,  which  time,  of  course,  varies  with  the  mass 
of  the  piece.  It  has  been  found  that,  owing  to  the  large  heat 
conductivity  of  steel,  the  surface  of  a  metallic  object  is  con- 
stantly somewhat  hotter  than  its  center,  but  colder  than  the 
furnace  atmosphere.  Both  differentials  decrease  as  the  steel 
nears  the  furnace  temperature;  therefore,  when  a  thermo-couple 
in  contact  with  the  surface  of  the  metal  registers  the  same  degree 
as  the  furnace  itself,  the  piece  is  heated  uniformly  and  is  ready 
for  quenching.  At  such  a  time  the  piece  can  be  seen  only  with 
difficulty,  as  it  radiates  heat  at  the  same  rate  as  the  furnace  walls 
themselves. 

As  a  matter  of  fact,  it  is  quite  a  difficult  thing  to  construct  a 
furnace  which  will  operate  at  a  uniform  temperature  and  a 
neutral  flame.  It  also  requires  good  judgment  so  to  place  the 
metallic  pieces  that  a  good  flow  of  heat  can  circulate  all  about 
them,  warming  all  parts  at  a  uniform  rate.  In  many  places 
baths  of  molten  salt  are  installed  which  have  many  obvious 
advantages  over  a  gas-  or  coal-fired  furnace.  Salt  baths  are 
better  than  molten  lead  baths,  because  they  do  not  alloy  with 
the  metal  nor  do  they  oxidize,  the  steel  pieces  readily  sink  in  the 
hot  liquid  and  do  not  have  to  be  held  below  the  surface.  On 
withdrawal  for  quenching,  the  objects  are  protected  from  surface 
oxidation  or  decarbonization  by  a  thin  film  of  adherent  salt, 
which  can  easily  be  washed  off. 

Warping  may  occur  in  the  heating  furnace  due  to  a  non- 
uniform  heating,  or  it,  with  its  partners  cracking  and  internal 
strain,  may  appear  after  the  quenching  operation,  but  for  the  self- 
same reason — variable  heat-transfer  rates.  The  ordinary  dif- 


HARDENING  OF  STEEL  143 

ferences  in  volume  due  to  expansion  with  increasing  tempera- 
ture are  accentuated  by  the  fact  that  there  is  a  large  contraction 
in  passing  thru  the  A  €3  range  and  a  corresponding  expansion 
at  Ars  transformation.  A  large  forging,  for  instance,  rapidly 
quenched  from  the  austenitic  condition,  will  act  somewhat  as 
follows:  The  surface  will  be  cooled  very  rapidly  thru  the  Ar 
ranges,  so  rapidly  that  the  normal  expansion  occurring  here  will 
be  suppressed.  The  drop  in  temperature  will  also  cause  a  further 
large  contraction,  and  the  net  result  is  a  cold  muff  shrunk  upon  a 
hotter  core.  This  core  will  cool  much  more  slowly  and  the  Ar 
transformations,  with  its  accompanying  expansion,  will  proceed 
(at  least  in  part),  further  stressing  the  outer  regions.  It  is 
small  wonder  that  quenched  forgings  warp,  split,  and  even 
explode  violently,  under  the  excessive  stresses  thus  produced. 
Large  pieces  should,  therefore,  be  counterbored,  mildly  quenched, 
and  annealed  immediately.  Boring  a  hole  in  the  center  of  forg- 
ings removes  metal  (which  is  usually  below  grade  because  of 
piping  and  segregation)  from  that  portion  of  the  piece  where 
even  good  metal  would  be  least  effective,  and  at  the  same  time 
provides  for  a  more  uniform  cooling  rate,  edge  to  center.  It 
is,  therefore,  seldom  that  even  a  piece  with  a  very  large  counter- 
bore  would  not  be  a  better,  stronger,  and  safer  piece  than 
originally.  Consequently,  such  practice  should  be  insisted 
upon  in  all  large  pieces  unless  absolutely  impossible  of  attain- 
ment. 

From  the  above  discussion,  it  is  evident  that  for  hand  work, 
symmetrical  sections  should  be  quenched  vertically  in  the 
direction  of  their  greatest  length.  Hollow  sections  should,  in 
addition,  have  a  stream  of  the  quenching  fluid  forced  up  thru 
the  interior  opening.  For  quantity  work,  certain  mechanical 
features  are  useful,  as  noted  in  Bullens'  "  Steel  and  its  Heat 
Treatment,"  ist  Edition,  pages  86  to  95. 

Special  Apparatus.  The  special  apparatus  needed  is  as  fol- 
lows: 

One  electrical  meter. 

Five-gallon  pail  for  quenching  bath. 


144  EXPERIMENTAL  GROUP  IV 

Supplies.     The  supplies  needed  are  as  follows: 

Ten  steel  rods  from  Experiment  No.  16. 
Two  steel  rods  from  Experiment  No.  17. 
Handful  of  waste. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Vises. 

Numerical  punches. 

Ice. 

Tank  of  quenching  oil. 

Impact  testing  machine. 

Scleroscope. 

Procedure,  a.  Take  twelve  pieces  of  steel  from  Experiments 
Nos.  16  and  17,  and  saw  one  notch  f  in.  from  the  end  of  each 
piece.  These  notches  must  be  gaged  and  cut  exactly  the  same 
depth  in  all  bars.  Punch-mark  the  short  ends  corresponding 
to  the  quenching  temperatures  of  procedure  e. 

b.  Place  the  bars  crosswise  in  the  oven   furnace,  separated 
somewhat  from  each  other,  with  that  one  bearing  the  lowest 
number  at  the  front.     Insert  your  calibrated  thermo-couple  in 
the  wrought-iron  protection  tube;    and  thrust   this  pipe  thru 
the  pyrometer  hole  in  the  furnace  in  such  a  manner  that  the  hot 
end  will  be  directly  above  and  preferably  resting  upon  the  first 
of  the  bars. 

c.  Heat  the  furnace  slowly  with  a  reducing  flame,  taking -about 
forty-five  minutes  to  attain  a  temperature  of  600°  C.     When 
this  degree  is  reached,  one  squad  member  should  open  the  door 
only  long  enough  for  another  to  grasp  the  end  of  the  first  bar 
with  tongs,  plunging  it  immediately  end  on  into  a  5-gallon  pail 
of  quenching  oil,  placed  close  up  to  the  furnace,  so  that  no  steps 
are  necessary.     Speed  in  transfer  is  essential.     Move  the  bar 
back  and  forth  sideways  in  the  bath  until  it  is  cold,  keeping  it 
constantly  submerged  in  a  vertical  position.     Remove,  wipe  off 
the  oil,  and  test  for  toughness  and  hardness  according  to  pro- 


HARDENING  OF  STEEL  145 

cedures/  and  g  of  Experiment  No.  17.  Paste  a  small  gummed 
label  around  each  fragment,  giving  its  carbon  content,  heat 
treatment,  hardness,  and  toughness. 

d.  During  the  testing,  the  furnace  tender  should  adjust  the 
next  bar  and  the  thermo-couple  to  juxtaposition,  and  increase 
the  temperature  slowly  so  that  at  least  ten  minutes  shall  inter- 
vene before   reaching  650°   C.,   when  procedure   c   should  be 
repeated.     Great  care  is  necessary  to  increase  the  temperature 
of  the  furnace  slowly,  and  to  get  the  bar  out  of  the  furnace  at 
the  exact  temperature — neither  more  nor  less. 

e.  Continue  in  this  manner,  quenching  bars  from  the  follow- 
ing temperatures: 

600°  C.  725°  C.  800°  C  900°  C. 

650  750  825  1000 

700  775  850  noo 

/.  Shut  off  the  gas  from  the  furnace  after  the  last  bar  has  been 
removed,  and  cool  it  rapidly  by  leaving  the  air  blast  on.  When 
it  has  dropped  to  a  black  heat,  range  all  the  long  bar-ends 
properly  in  the  furnace,  and  anneal  carefully  at  the  temperature 
which  gives  the  minimum  grain  size.  Cool  over  night  in  the 
furnace. 

g.  Plot  on  a  sheet  of  coordinate  paper  one  curve  showing 
the  relation  of  hardness  to  quenching  temperature,  and  another 
showing  a  like  relation  for  toughness  to  quenching  temperature. 
Use  degrees  Centigrade  rather  than  dial  readings  for  abscissae 
and  locate  each  quenching  by  a  small  circle.  Letter  on  the  sheet 
the  squad  number,  personnel  and  the  carbon  content  of  the 
steel.  Submit  this  sheet  of  curves  to  a  laboratory  officer  for 
inspection  and  O.K.,  and  then  pin  the  sheet  on  the  proper 
bulletin  board  for  reference  by  the  rest  of  the  class. 

Queries,  a.  Each  student  should  make  in  India  ink  the 
curves  described  in  procedure  g  above.  Locate  in  an  appropriate 
manner  the  position  of  the  Ac  transformation  ranges.  Discuss 
the  relation  of  hardness  to  transformation  ranges  as  evidenced 
by  this  experiment. 


146  EXPERIMENTAL  GROUP  IV 

b.  Compare  the  crystalline  grain  shown  by  the  fracture  of 
the  quenched  pieces  from  this  experiment  to  those  from  Experi- 
ment No.  17.     What  general  difference,  if  any,  is  exhibited  by 
quenched  pieces  from  those  annealed  at  the  same  temperature. 

c.  Make  up  an  equilibrium  diagram  for  steel  on  coordinate 
paper  in  light  black  lines,  following  Fig.  23,  page  131.     Plot  on 
this  diagram  the  hardness  numeral  of  all  the  fragments  tested 
by  the  laboratory  squads  as  posted  on  the  bulletin  board.     Draw 
contour  lines  of  equal  hardness  in  red. 

d.  What  is  the  constitution  of  a  .05  carbon  steel  (five-point 
steel)  at  740°  C.,  850°  C.,  and  1000°  C.?    Are  these  states  pre- 
served in  the  cold  after  quenching  in  oil?    What  conclusions  can 
be  drawn  from  the  curves  of  query  c  as  to  the  hardness  of  wrought 
iron  if  quenched  from  these  temperatures? 

e.  Why  is  the  lowest  heat  giving  the  hardening  effect  the 
best  heat  to  use? 


EXPERIMENT  NO.  19 
QUENCHING  MEDIA 

Object.  The  object  of  this  experiment  is  to  study  the 
hardening  power  of  various  liquids. 

General  Explanation.  When  a  piece  of  hot  iron  is  plunged 
into  a  cold  liquid,  the  latter  dances  against  the  surface  of  the 
metal  in  much  the  same  manner  as  drops  of  water  dance  on  a  hot 
stove.  The  quenching  fluid  comes  into  contact  with  the  heated 
surface  perhaps  momentarily,  but  it  immediately  vaporizes, 
and  the  liquid  for  the  most  part  is  held  away  by  a  thin  film  of  gas. 
The  actual  transfer  of  heat  (see  page  105,  Experiment  No.  14) 
from  the  hot  metal  to  the  cold  liquid  takes  place  in  the  first 
place  by  convection  currents,  where  gaseous  bubbles  are  driven 
away  into  the  colder  surroundings,  there  to  escape  or  be  con- 
densed; secondly,  by  radiation  thru  this  gaseous  envelope, 
and  thirdly,  by  conduction  across  the  following  system — metal: 
gas  interface,  gas  film,  gas: liquid  interface.  The  relative  impor- 
tance of  the  three  methods  are  about  in  the  order  as  stated — 
the  first  (convection)  probably  removing  a  large  part  of  the  heat, 
the  third  (conduction)  removing  comparatively  little,  owing  to 
the  great  resistivity  of  the  system  due  to  the  large  coefficients 
of  internal  transfer  at  the  two  interfaces.  The  heat  loss  by 
convection  is  obviously  accelerated  by  moving  the  quenched 
metal  about  in  the  bath. 

We  may  say,  therefore,  that  the  quenching  power  of  a  fluid 
depends,  to  a  large  extent,  upon  its  total  heat  to  the  boiling 
point,  its  latent  heat  of  vaporization,  and  its  coefficient  of 
emissivity  (page  112).  A  bath  which  absorbs  much  heat  per  unit 
volume  to  bring  the  contact  firm  to  the  boiling  point,  then  a 
further  large  amount  to  vaporize  this  hot  liquid,  and  is  thin  or 
mobile  enough  to  allow  free  passage  of  gas  bubbles  away  from 

147 


148  EXPERIMENTAL   GROUP  IV 

the  hot  surface  into  the  colder  surroundings,  will  cool  heated 
articles  quickly. 

Thousands  of  different  fluids  have  been  tried  as  quenching 
baths.  Those  most  commonly  used  are  water,  various  salt 
solutions,  different  kinds  of  mineral  or  organic  oils,  and  finally, 
molten  metal  or  salt  baths.  A  tank  of  ordinary  tap  water  is 
one  of  the  quickest  quenching  baths  known,  being  exceeded  only 
by  salt  solutions  and  water  jets;  in  fact,  it  produces  an  action 
so  drastic  that  it  is  unsafe  to  use  on  work  with  more  than  twenty 
points  of  carbon  except  in  the  hands  of  experts.  Oil  baths  are 
much  milder,  and  their  cooling  speed  is  less  dependent  upon  the 
temperature  of  the  bath.  In  fact,  some  sticky  oils  quench  more 
rapidly  when  hot  than  when  cold,  owing  to  the  greater  viscosity 
at  low  temperatures.  Molten  metals  or  salts  cool  hot  steel 
quite  slowly,  but  are  invaluable  in  the  heat  treatment  of  modern 
high-speed  steel.  Many  secret  compounds  on  the  market 
are  said,  especially  by  their  salesmen,  to  be  capable  of  curing 
any  hardening  room  difficulty.  As  is  the  case  of  patent  cements 
(Experiment  No.  23),  most,  if  not  all,  such  panaceas  are  worth- 
less; educated  people  shun  "  cure-alls." 

Good  quenching  baths  should  have  arrangements  to  main- 
tain a  uniform  temperature.  This  may  be  effected  by  coiling 
cold-water  pipes  around  the  sides  of  the  tanks;  or,  better,  by 
circulating  the  quenching  medium  itself.  Stirring  the  oil  by 
means  of  compressed  air  should  be  avoided,  on  account  of  the 
oxidation  of  the  oil  which  usually  proceeds,  and  the  danger  of  a 
stream  of  air  bubbles  bathing  the  side  of  a  hot  piece  during 
quenching,  with  the  consequent  formation  of  a  soft  spot. 

Special  Apparatus .   The  special  apparatus  needed  is  as  follows : 

Five  5-gallon  pails. 

One  large  gas  burner. 

One  large  tripod. 

Two  pieces  of  gas  tubing,  10  feet  long. 

One  300°  C.  mercury  thermometer,  metal  cased. 

One  electrical  meter. 


QUENCHING   MEDIA  149 

Supplies.     The  supplies  needed  are  as  follows: 

Four  pounds  of  salt  (NaCl). 

Seven  bars  from  Experiment  No.  18. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Vises. 

Alphabet  punches. 

Ice. 

Tank  of  annealing  oil. 

Lead  pot  at  400°  C.  with  pyrometer  equipment. 

Procedure,  a.  Call  an  instructor's  attention  to  the  curve 
constructed  in  Experiment  No.  18,  procedure  g,  and  decide  with 
him  the  correct  quenching  temperature  for  that  particular  steel. 
Notch  seven  pieces  of  steel  from  Experiment  No.  18,  three- 
quarters  of  an  inch  from  the  end,  and  to  exactly  the  same  depth 
in  each  bar.  Punch-mark  the  short  ends  corresponding  to  the 
quenching  media  used. 

b.  Arrange  the  thermo-couple  in  the  furnace  as  directed  in 
procedure  d  of  Experiment  No.  17,  and  heat  the  oven  furnace 
to  the  proper  quenching  temperature.     Hold  the  temperature 
at  this  degree  for  twenty  minutes  with  a  reducing  flame,  before 
putting  the  bars  into  the  furnace.     One  member  of  the  squad 
should  give  his  entire  attention  to  the  furnace  control. 

c.  Place  the  seven  bars  endwise  in  the  furnace,  notches  to 
the  rear,  so  that  they  may  be  equally  heated  in  all  parts,  and 
allow  to  remain  thirty  minutes,  or  longer  if  necessary  to  attain 
the   temperature   of   the   furnace.     The    flame    need    not    be 
adjusted  during  the  heating  if  the  furnace  was  at  equilibrium 
before  the  bars  were  introduced. 

d.  During  the  heating,  arrange  nearby  quenching  baths  as 
follows,  each  in  a  5-gallon  pail: 

Ten  per  cent  salt  solution. 
Ice  water. 


150  EXPERIMENTAL  GROUP  IV 

Tap  water. 
Boiling  water. 
Annealing  oil  at  200°  C. 

Also  see  that  the  lead  pot  is  ready  for  use,  and  at  a  temperature 
of  400°  C. 

e.  Quench  one  bar  in  each  medium  after  procedure  c  of 
Experiment  No.  18.  Close  the  furnace  between  times  long 
enough  for  the  pyrometer  to  recover  the  correct  temperature. 
Test  each  piece  for  hardness  and  toughness  according  to  pro- 
cedures /  and  g  of  Experiment  No.  17.  In  preparing  for  the 
hardness  test,  grind  the  pieces  very  slowly,  keeping  the  bars  cold. 
Paste  a  small  gummed  label  around  each  fragment,  giving  its 
carbon  content,  heat  treatment,  hardness,  and  toughness. 
Preserve  all  the  pieces  for  reference. 

/.  Heat  the  seventh  bar  in  the  furnace  to  the  maximum 
temperature  attainable,  and  quench  in  iced  brine.  Test  as  in 
procedure  e,  above. 

g.  Shut  off  the  gas  after  the  last  bar  has  been  removed,  and 
cool  the  furnace  rapidly  by  leaving  the  air  blast  on.  When  it 
has  dropped  to  a  black  heat,  range  all  the  long  bar-ends  properly 
in  the  furnace,  and  anneal  carefully  at  the  temperature  which 
gives  the  minimum  grain  size.  Cool  overnight  in  the  furnace. 

Queries,  a.  Construct  a  neat  tabulation  of  the  results, 
including  the  hardness  and  toughness  of  oil-quenched  steel  from 
Experiment  No.  17. 

b.  Why  should  a  quenching  in  brine  give  a  greater  hardness 
than  a  quenching  in  water  of  the  same  temperature? 

c.  Define    "  toughness."     Is    there    any    relation    between 
hardness  and  toughness  in  carbon  steels? 

d.  Give  two  reasons  why  the  hardness  resulting  from  water 
quenching  should  vary  inversely  as  the  temperature  of  the 
quenching  bath. 

e.  Why  should  the  hardness  of  a  high-carbon  bar  quenched 
from  1200°  C.  in  iced  brine  be  less  than  that  of  the  same  bar 
quenched  from  850°  C.  in  cold  water? 


QUENCHING   MEDIA  151 

/.  Outline  a  system  for  circulating  and  cooling  the  quench- 
ing oil  for  a  battery  of  hardening  ovens. 

g.  What  is  modern  high-speed  steel?  Outline  the  heat 
treatment  of  such  tools  recommended  by  Frederick  W.  Taylor. 

h.  Why  does  procedure  e,  above,  specify  "grind  cold?" 


EXPERIMENT  NO.  20 
TEMPERING  AND  TOUGHENING 

Object.  The  object  of  this  experiment  is  to  study  the  effect 
of  reheating  a  hardened  steel. 

General  Explanation.  When  carbon  steels  are  heated  above 
the  transformation  range  into  the  austenitic  area,  the  various 
aggregations  of  ferrite  and  cementite  crystals  normally  present 
in  slowly  cooled  steels  are  converted  into  a  uniform  solid  solution, 
austenite.  The  exact  reverse  of  this  happens  on  slow  cooling, 
a?  was  indicated  in  Experiment  No.  16.  All  previous  structure 
is  consequently  obliterated  by  a  sufficient  heating,  and  upon  sub- 
sequent rapid  cooling  by  quenching,  the  usual  conversion  of 
austenite  (stable  only  at  high  temperatures),  back  into  the 
aggregate  of  ferrite  and  cementite  is  prevented,  at  least  in  part, 
because  of  lack  of  time  afforded  at  the  transformation  ranges. 

Time  is  an  essential  to  this  decomposition,  for  the  gamma 
iron  existing  in  the  austenite  must  change  thru  the  beta  into 
the  alpha  modification,  and  the  ferrite  and  cementite  must 
further  separate  and  coagulate  into  the  state  recognized  as 
pearlite.  Molecular  rearrangement  and  migration  in  the  solid 
is  possible  only  if  a  sufficiently  elevated  temperature  allows  the 
molecules  the  requisite  freedom  of  movement.  Should  cooling 
be  so  rapid  as  to  lock  the  molecules  tightly  together  in  the  cold 
steel  before  any  change  proceeds,  pure  austenite  may  be  pre- 
served and  examined  in  the  cold  (Fig.  30).  In  the  ordinary 
practice  of  hardening  steels  as  described  in  Experiments  Nos. 
1 8  and  19,  the  quenching  is  not  so  drastic,  and  the  transforma- 
tion of  austenite  back  to  ferrite  and  cementite  is  more  or  less 
completely  effected,  giving  rise  to  certain  transitory  forms  which 
are  known  as  "  martensite,"  "  troostite,"  "  sorbite,"  and,  finally, 

152 


TEMPERING  AND  TOUGHENING  153 

the  various  kinds  of  pearlite.     (See  Mills,  "  Materials  of  Con- 
struction," pages  430  to  438.) 

The  phenomena  of  hardening  plain  carbon  steels  by  rapid 
cooling  and  the  softening  which  occurs  by  a  subsequent  moderate 
reheating,  undoubtedly  are  intimately  associated  with  this 
delayed  transformation.  A  complete  explanation  of  hardening 
must  account  for  other  facts,  such  as  these:  The  hardness  of 
certain  alloy  steels  high  in  carbon,  manganese,  or  nickel,  is  con- 
siderable even  after  slow  cooling.  Some  manganese  steels  are 


FIG.   30. — Patch  of  Austenite  from   Eutectoid   Steel.     22oX.     Quenched   from 
800°  C.  in  Iced  Brine. 

hard  if  cooled  slowly,  but  softer  if  quenched.  Another  alloy 
steel  may  be  hardened  in  three  ways :  Either  by  cooling  in  liquid 
air,  by  a  moderate  tempering,  or  by  attempting  to  machine  it. 
Pure  iron  and  low-carbon  steels  are  hardened  materially  by  cold 
working. 

A  considerable  analogy  exists  between  hardening  and  cold 
working  (which  latter  causes  internal  stresses  and  strains), 
inasmuch  as  both  increase  hardness,  brittleness,  and  strength. 
Some  scientists  have,  therefore,  attempted  to  explain  quenching 
phenomena  by  attributing  the  resulting  hardness  to  the  internal 
stresses  caused  by  the  shrinkage  of  the  shell  and  the  dilation  of 


154  EXPERIMENTAL   GROUP  IV 

gamma  into  beta  iron  (Andre  Le  Chatelier).  McCance  thinks 
that  supercooled  gamma  iron  is  held  in  its  original  octahedral 
crystalline  orientation  under  great  intermolecular  stress;  while 
Humphrey  believes  that  the  transformation  of  iron  has  actually 
proceeded  far  enough  to  lose  its  octahedral  symmetry  without 
yet  attaining  the  cubic  orientation  of  alpha  iron.  The  resulting 
iron  is,  therefore,  in  an  amorphous  condition,  which  we  know  to 
be  harder  and  stronger  than  a  crystalline  state. 

These  various  hypotheses  are  incapable  of  explaining  the 
hardness  of  slowly  cooled  and  annealed  alloy  steels,  altho 
internal  strain,  doubtless,  produces  considerable  hardness  under 
certain  conditions.  Likewise,  hypotheses  based  on  the  presence 
of  carbon  or  some  hard  carbide  are  insufficient  to  explain  the 
great  hardness  of  low-carbon  alloy  steels  or  the  change  in  hard- 
ness on  tempering  high-carbon  steels.  As  a  matter  of  fact,  a 
massive  carbide  FesC  has  been  prepared  and  found  to  possess 
only  moderate  hardness. 

Osmond's  allotropic  theory  thus  seems  most  nearly  to  cover 
the  facts.  It  rests  on  the  recognition  of  three  unique  states  of 
iron,  viz.:  gamma  iron,  dense;  beta  iron,  hard;  and  alpha  iron, 
magnetic.  When  the  steel  cools  from  the  gamma  condition,  the 
allotropic  changes  may  be  regarded  as  taking  place  in  two  steps; 
the  first  characterized  by  a  dilation  and  hardening  from  the 
gamma  state  into  beta  iron;  and  the  second  by  softening  and 
magnetization  from  beta  into  alpha  iron.  These  steps  overlap 
to  various  degrees  in  quenching  at  different  speeds,  and  cause 
independent  variations  in  magnetism  against  hardness.  The 
latter,  in  fact,  may  be  anything  from  the  Brinell  hardness  125  of 
gamma  iron,  up  to  the  800  of  beta,  or  down  on  the  other  side  of 
the  maximum  to  the  75  of  alpha  iron. 

According  to  this  theory,  a  soft  steel  may,  therefore,  be 
austenitic,  containing  gamma  iron,  or  pearlitic,  with  alpha  iron. 
Alloy  steels  are  often  austenitic,  with  their  Ae  ranges  depressed 
to  nearly  room  temperatures.  Such  a  steel  on  moderately  slow 
cooling  ordinarily  would  be  in  a  slightly  supercooled  austenitic 
condition,  and  could  be  hardened  either  by  further  cooling  in  a 


TEMPERING  AND  TOUGHENING  155 

refrigerant,  causing  the  beta  iron  to  form  (martensite),  or  by  a 
moderate  reheating  to  a  temperature  below  the  transformation 
range  where  the  time  and  molecular  mobility  would  be  sufficient 
to  effect  the  same  conversion,  or,  lastly,  by  the  molecular  activity 
induced  by  the  overstraining  of  machining,  forging,  or  other  cold 
working  operations. 

Osmond's  theory  is  also  competent  to  explain  annealing  and 
toughening  practice.  A  quickly  quenched  carbon  steel  is  mostly 
martensitic (Fig.  31), which  metaral  is  a  solid  solution  of  beta  iron 


FIG.   31. — Patch  of  Martensite  from  Eutectoid  Steel.     2ooX.     Quenched  from 
800°  C.  in  Iced  Brine. 

and  cementite,  hard  and  brittle.  Moderate  reheating  or  anneal- 
ing changes  this  structure  largely  into  troostite  (Figs.  32  and  33), 
which  is  a  partly  transformed  martensite,  possessing  much  of  the 
hardness  of  martensite,  but  with  a  largely  increased  toughness 
and  shock  resistance.  This  toughness  is  the  chief  characteristic 
of  the  next  metaral  in  the  transformation  series,  sorbite  (Figs. 
34  and  35),  which  is  merely  martensite  wholly  transformed  into  a 
mixture  of  ultramicroscopic  crystals  of  ferrite  (alpha  iron)  and 
cementite  (FeaC). 

The  word  tempering  should  be  restricted  to  denote  a  moderate 
reheating,  up  to  about  350  C.,  forming  troostitic  steel,  while 


156 


EXPERIMENTAL   GROUP  IV 


FIG.  32. — Martensite  (light  areas)  pass- 
ing into  Troostite  (dark  areas).  22oX. 
Eutectoid  Steel,  Quenched  from 
800°  C.,  tempered  at  275°  C. 


FIG.  33. — Martensite  (light  needles) 
passing  into  Troostite  (dark  patches). 
i3oX.  From  a  piece  of  Eutectoid 
Steel  Electrically  Welded. 


FIG.  34. — Sorbite  (dark  patches)  pass-        FIG.    35.* — Carbon    Steel,      i.co    per 


ing  into  Pearlite  (wavy  striations). 
Light  Areas  are  Patches  of  Ferrite. 
22oX.  From  a  piece  of  Hypoeutec- 
toid  Steel  Electrically  Welded. 


cent  Carbon.  15  oX.  Osmond. 
Pearlite,  laminated,  passing  into 
sorbite,  dark  and  formless. 

*  Reproduced  by  permisison  from  Saveur, 
"  Metallography  and  Heat  Treatment  of 
Iron  and  Steel." 


TEMPERING  AND  TOUGHENING  157 

"  toughening  "  represents  the  practice  of  reheating  hardened 
carbon  steels  from  350°  C.  up  "to  just  below  Ac\,  and  forms 
sorbitic  steel;  while  "  annealing  "  refers  to  a  heating  for  grain 
size  at  or  above  the  transformation  ranges,  followed  by  a 
slow  cooling.  Any  of  these  operations  not  only  allows  the  trans- 
formations from  austenite  to  pearlite  to  proceed,  but  also  relieves 
internal  stresses  in  the  steel. 

Tempering  heats  have  been  gaged  since  time  immemorial  by 
the  distinctive  colors  of  the  thin  oxide  films  which  form  on 
bright  steel  as  it  is  heated  from  200°  C.  to  350°  C.  A  skilled 
artisan  can  estimate  these  colors  to  a  tolerance  of  a  few  degrees, 
which,  indeed,  is  necessary  for  the  production  of  uniform  results. 
The  disadvantages  of  this  handy  method  are  obvious,  however. 
Leaving  aside  the  effect  of  the  skill  of  the  operator,  that  is,  the 
"  personal  equation,"  and  the  effect  of  the  varying  lights  due  to 
shop  and  weather  conditions,  it  should  be  borne  in  mind  that 
tempering  by  colors  places  reliance  on  what  is  strictly  a  surface 
phenomenon.  The  rate  of  heating,  the  time  at  the  maximum 
heat,  the  mass  and  configuration  of  the  steel  object  all  affect 
the  color  indications,  and  consequently  the  uniformity  and 
homogeneity  of  the  results.  Ordinary  usage  is  to  heat  the  bar 
rather  rapidly  in  a  furnace  which  is  considerably  above  the  desired 
degree.  In  order  to  make  sure  that  the  temperature  does  not 
mount  too  high,  it  is  then  necessary  to  quench  the  piece  after 
the  desired  color  appears  on  the  surface.  This  quenching 
induces,  in  part,  the  internal  stresses  which  a  proper  tempering 
followed  by  a  slow  cooling  would  relieve. 

Steam  plates,  sand  baths,  molten  salt,  and  metal,  are  there- 
fore used  in  the  most  modern  installations,  adequately  con- 
trolled by  pyrometers  and  operating  uniformly  at  the  proper 
temperature.  With  such  equipment  it  is  easy  thoroly  and 
properly  to  heat  metal  pieces  even  of  irregular  cross-section. 
The  subsequent  cooling  can  then  be  as  slow  as  desired. 

Special  Apparatus.  The  special  apparatus  needed  is  as  fol- 
lows : 


158  EXPERIMENTAL  GROUP  IV 

Two  riddles;  one  i-in.;  one  J-in. 

Hatchet. 

One  5-gallon  pail  for  quenching  bath. 

One  deep  metal  pan  for  annealing  bath. 

Wire  basket  for  holding  metal. 

One  300°  C.  mercury  thermometer,  metal  cased. 

One  electrical  meter. 

Supplies.     The  supplies  needed  are  as  follows: 

Eleven  bars  from  Experiments  17,  1 8  and  19. 
Laboratory  Equipment.     The  laboratory  equipment  needed 
is  as  follows: 

Ice. 

Coke. 

Bucking-board  and  muller. 

Kindling  wood. 

Anvil  and  blacksmith's  tools. 

Emery  wheel. 

Vises. 

Numerical  punches. 

Scleroscope. 

Impact  machine. 

Drop-hammer,  with  anvil  of  mild  steel. 

Annealing  oil. 

Lead  pot  and  pyrometer  equipment. 

Portable  rivet  forge. 

Procedure,  a.  Make  a  coke  fire  in  the  portable  forge  as 
follows:  Crush  about  i  cu.  ft.  of  coke  thru  the  £-in.  riddle, 
screening  out  the  fines  with  a  J-in.  riddle.  Wet  the  fines  and 
bank  them  around  the  sides  of  the  forge,  forming  a  saucer- shaped 
depression  with  the  tuyere  at  the  bottom.  Cut  fine  kindlings 
and  build  up  a  good  bed  of  hot  wood  embers  with  a  gentle  blast, 
gradually  adding  more  and  more  of  the  f-in.  coke  with  the  wood 
until  a  solid  bed  of  glowing  coke  remains. 

b.  Insert  eleven  steel  bars  into  the  hot  bed  of  coals,  one  at  a 
time,  heating  about  2  in.  at  the  end  to  a  bright  red,  and  then 


TEMPERING  AND   TOUGHENING  159 

forge  a  round  point  on  the  bar.  Guard  against  overheating  and 
burning  the  bar,  and  continue  the  hammering  to  a  low  heat. 
Do  not  start  the  heating  of  the  second  bar  until  the  first  is  ham- 
mered cold.  Finish  the  point  on  a  coarse  emery  wheel. 

c.  Discuss  the  results  of  Experiments  Nos.  18  and  19  with  an 
instructor,  and  decide  with  him  the  correct  quenching  tempera- 
ture and  medium.     Notch  each  bar  f  in.  from  the  square  end  to 
exactly  the  same  depth,  punch  mark  the  ends  and  bodies  of  the 
bars  with  the  reheating  temperatures  used  in  this  experiment, 
heat  the  bars  according  to  procedures  b  to  d  of  Experiment  No.  19, 
and  quench  according  to  procedure  c  of   Experiment  No.  18. 
Grind  the  square  end  carefully,  and  test  each  bar  for  hardness. 
Should  the  hardness  of  the  different  bars  vary  more  than  15  per 
cent  the  hardening  must  be  repeated  until  this  tolerance  is 
attained. 

d.  Arrange  a  pan  of  boiling  water  over  a  gas  burner,  place 
one  bar  in  the  wire  basket,  and  plunge  it  into  the  liquid.     The 
bar  being  reheated  must  not  touch  the  bottom  or  sides  of  the 
tank,  and  the  annealing  fluid  must  be  in  constant  circulation  on 
all  sides  of  the  piece.     After  fifteen  minutes,  remove  and  cool 
in  the  air. 

e.  Grind  a  sharp  point  with  a  fine  emery  wheel,  and  test  its 
condition  by  holding  the  bar  upright  under  the  drop-hammer, 
with  the  bottom  block  replaced  by  a  block  of  mild  steel.     Raise 
the  hammer  i  in.,  release,  and  examine  the  condition  of  the  point 
after  the  blow.     Repeat  the  drop  from  2  in.,  3  in.,  4  in.,  etc., 
until  the  point  breaks,  turns  over,  flattens,  or  fails  in  some  other 
manner.     Test  the  square  end  with  the  impact  machine  and 
scleroscope  according  to  procedures/  and  g  of  Experiment  No.  17. 
Paste  a  small  gummed  label  around  both  fragments,  giving  the 
carbon  content,  heat  treatment,  hardness  and  toughness.     Pre- 
serve all  pieces  for  reference. 

/.  Reheat  four  other  pieces  in  a  pan  of  oil,  one  to  the  follow- 
ing temperatures, 

200°  C.          250°  C.          300°  C. 


160  EXPERIMENTAL   GROUP  IV 

stirring  the  oil  constantly,  and  making  sure  that  the  piece  is  not 
overheated.  These  pieces  may  be  withdrawn  from  a  rising 
temperature  at  the  proper  point  if  at  least  twenty  minutes  is 
consumed  in  covering  the  intervals  between.  Cool  each  piece 
in  air,  and  test  as  in  procedure  e  above.  The  fourth  bar  should  be 
held  in  the  hot  oil  bath  at  300°  C.  for  one  hour  (being  extremely 
careful  to  maintain  a  uniform  temperature)  and  then  air  cooled 
and  tested  as  the  others. 

g.  Reheat  six  other  pieces  in  the  lead  pot,  one  to  each  of 
the  following  temperatures: 

400°  C. 
500°  C. 


Use  the  precautions  noted  in  procedure  /  and  test  each  bar  as 
usual. 

h.  Draw  curves  on  coordinate  paper  showing  the  variation  in 
hardness  and  toughness  with  the  reheating  temperature  as 
determined  by  the  results  of  this  experiment.  Post  this  on  the 
bulletin  board,  and  exhibit  the  results  of  the  tests  to  an  instructor. 

Queries,  a.  Draw  curves  in  India  ink  on  coordinate  paper 
showing  the  variation  in  hardness  and  toughness  with  the 
reheating  temperature  as  determined  by  the  results  of  this 
experiment.  Show  in  color  on  the  same  sheet  a  curve  of  hard- 
ness against  annealing  temperature  derived  from  Experiment 
No.  17.  Discuss  reasons  for  similarities  or  differences  in  the 
results  of  Experiments  Nos.  17  and  20. 

b.  Make  up  an  equilibrium  diagram  for  steel  on  coordinate 
paper  in  light  black  lines,  following  Fig.  23,  page  131.  Plot  on 
this  diagram  the  toughness  of  all  the  fragments  tested  by  the 
laboratory  squads  as  posted  on  the  bulletin  board.  Draw  con- 
tour lines  of  equal  toughness  in  red 


TEMPERING  AND  TOUGHENING  161 

c.  What  effect  will  the  speed  of  heating  from  the  cold  to  the 
tempering  or  toughening  temperature  have  upon  the  results? 

d.  What  effect  will  the  speed  of  cooling  have? 

e.  How  will  the  length  of  time  at  the  reheating  temperature 
affect  the  results  of  the  operation? 

/.  Assuming  that  the  hardened  steel  bars  of  eutectoid  com- 
position have  a  structure  essentially  of  martensite  with  but  a 
small  amount  of  austenite,  what  will  be  the  structure  persisting 
after  each  reheating? 


EXPERIMENT  NO.  21 
TOOL  MAKING 

Object.  The  object  of  this  experiment  is  to  apply  the 
knowledge  gained  in  previous  experiments  in  making  a  center 
punch  and  a  cold  chisel. 

General  Explanation.  Important  as  are  applications  of  the 
complex  alloys  known  as  "  high-speed  steels,"  there  are  now, 
and  doubtless  always  will  be,  enormous  numbers  of  tools,  machine 
parts,  and  structural  members  which  are  made  of  plain  carbon 
steels.  Even  some  very  heavy-duty  tools  will  continue  to  be 
made  of  the  simpler  carbon  steels,  since  they  can  be  hardened 
to  a  much  higher  degree  than  can  the  modern  high-speed  tools, 
which  latter  are  pre-eminent  for  most  metal  cutting  purposes 
not  because  of  their  intrinsic  hardness,  but  because  of  their 
ability  to  retain  their  moderate  hardness  when  cutting  so  fast 
that  the  sharp  edge  is  heated  to  an  annealing  temperature. 

Among  makers  and  vendors,  simple  carbon  tool-steels  are 
classed  by  "  grade,"  and  "  temper."  The  word  grade  is  qual- 
ified by  many  adjectives,  some  with  more  or  less  special  or 
cryptic  meanings,  but,  in  general,  it  has  to  do  with  the  process 
and  care  with  which  the  steel  is  made. 

The  more  important  grades  may,  therefore,  be  listed  as 

Crucible  steel, 
Open-hearth  steel, 
Bessemer  steel. 

The  grade  adopted  for  a  particular  tool  depends  upon  the  pre- 
cision and  life  expected  of  the  intrument,  and  the  cost  of  the 
tool-maker's  labor.  Crucible  steels  are  used  for  such  things  as 
fine-edged  tools  and  saws,  fine  springs,  rock  drills,  precision  tool 
parts,  and  high-speed  weaving  machinery  parts.  Car  and  wagon 

162 


TOOL  MAKING  163 

springs,  heavy  machinery  and  locomotive  parts  can  be  made 
amply  strong  of  good  open-hearth  steel,  while  sledges,  picks  and 
other  coarse,  battering  hand-tools  can  be  satisfactorily  made  of 
Bessemer  billets. 

Just  why  a  crucible  steel  should  be  better  than  an  open- 
hearth  steel  of  the  same  analysis  has  been  productive  of  much 
argument,  and  it  is  still  a  contested  point,  especially  by  open- 
hearth  steel  makers.  Metcalf  thinks  it  proven  that  the  lower 
oxygen  and  nitrogen  content  of  crucible  steels  makes  them 
superior  to  the  other  grades. 

The  temper  of  a  steel  refers  to  the  carbon  content  of  the 
material.  This  should  preferably  be  noted  by  "  points,"  but, 
unfortunately,  a  53-point  steel  (containing  0.53  per  cent  of  car- 
bon) may  locally  be  called  something  like  "  No.  3  temper." 
A  list  of  the  approximate  carbon  content  and  tempering  heats 
favored  for  many  tools  and  machine  parts  is  appended,  taken 
largely  from  Bullens,  "  Steel  and  its  Heat  Treatment,"  Chapter 
XVI. 

Carbon  Per  Cent.  Tools.  Tempering  Heat. 

Possessing  extreme  hardness  in  cutting  edge.     Toughness  a  slight  factor: 

i .  50  Lathe  tools  for  tempered  gun  f orgings 

i .  40  Lathe  tools  for  chilled  rolls 

Graver  tools 215 

Brass- working  tools 

i .  30  General  lathe  tools 

General  slotter  tools 

General  planer  tools 215 

Razors 

Drawing,  trimming  and  cutting  dies 240 

Mandrels 

Granite  points 

Scale  pivots 

Bush  hammers 215 

Peen  hammers 215 

Files 

Ball  races 

Great  hardness,  combined  with  some  toughness: 

i .  20  Twist  drills 250 

Small  taps 225 

Screw  and  threading  dies 225 


164  EXPERIMENTAL  GROUP  IV 

Carbon  Per  Cent.  Tools.  Tempering  Heat. 

Cutlery 225 

Cold  stamping  dies 240 

Leather-cutting  dies 225 

Cloth  and  glove  dies 240 

Nail  dies 240 

Jeweller's  rolls  and  dies 240 

i .  10  Milling  and  circular  cutters 225 

Wood-working  and  -forming  tools. 

Small  punches 240 

Taps 225 

Cup  and  cone  steel 250 

Small  springs 300 

Anvils 

Toughness  and  cutting  edge  about  equal  considerations: 

i .  oo  Reamers 240 

Drifts 265 

Broaches 275 

Large  milling  cullers 225 

Saw  swages 

Springs 300 

Rock  and  channeling  drills 225 

Large  cutting  and  trimming  dies 240 

Good  cutting  edge,  but  toughness  an  important  factor: 

o. 90  Hand  chisels 270 

Chipping  chisels 270 

Punches 240 

Blanking  punches  and  dies 240 

Drop  dies  for  cold  work 240 

Small  shear  knives 225 

Tough  tools  for  withstanding  shocks: 

o. 80  Large  shear  knives 225 

Large  chisels 270 

Hammers 215 

Sledges 

Cold  sets 270 

Forging  dies 240 

Hammer  dies 240 

Boiler-maker's  tools 270 

Mason's  tools 240 

Churn  drills 225 

o.  70  Track-layer's  tools 

Cupping  tools 250 

Hot  sets 

Set  screws .  . 


TOOL  MAKING  165 

Carbon  Per  Cent.  Tools.  Tempering  Heat. 

Great  toughness  required,  but  still  suitable  for  hardening  and  tempering: 

o.  60  Hot  work  battering  tools 280 

Bolt  and  rivet  headers 

Hot  drop-forging  dies 

Rivet  sets 

Fullers 

Wedges 

Toughness  the  prime  consideration : 

o.  50  Machinery  parts 

Hot  dies  for  bolt-making  machines 

Of  course  it  should  be  remembered  that  the  above  classifi- 
cation is  by  no  means  final — the  carbon  content  may  vary  con- 
siderably with  the  presence  of  some  other  alloying  element; 
while  the  tempering  heat  especially  should  be  carefully  adjusted 
to  fit  the  needs  of  each  class  and  size  of  tools  or  machine,  as 
well  as  varied  to  conform  with  the  hardness  and  other  physical 
and  chemical  properties  of  the  materials  worked  upon. 

Supplies.     The  supplies  needed  are  as  follows: 

One  6-in.  piece  of  f-  or  f-in.  eutectoid  steel. 
One  6-in.  piece  of  f-in.  eutectoid  steel. 

Laboratory  Equipment.  The  laboratory  equipment  needed  is 
as  follows: 

Ice. 

Quenching  media. 

Scleroscope. 

Annealing  Oil. 

Coke. 

Bucking-board  and  muller. 

Anvil  and  blacksmith's  tools. 

Emery  wheel. 

Forge. 

Procedure,  a.  After  the  student  has  performed  the  pre- 
ceding experiments,  he  should  be  able  to  draw  up  the  proper 
procedure  to  make  a  center  punch  and  a  cold  chisel.  Make  up  a 


166  EXPERIMENTAL   GROUP  IV 

brief  outline  of  the  various  steps  in  the  process  and  submit  it  to 
an  instructor  for  O.K. 

b.  Plan  the  work  and  make  out  two  slips,  one  calling  for  the 
complete  list  of  special  apparatus  required,  and  the  second  calling 
for  all  the  supplies  desired.     Procure  these  things  of  the  stock 
keeper,  signing  and  leaving  your  slip  as  a  receipt. 

c.  Make  good,  sharp,  tools,  of  finished  appearance,  and  with 
the    correct    hardness    and    toughness.     Submit    them    to    the 
instructor  for  testing  and  O.K. 

Queries,  a.  Write  up  the  experiment  after  the  style  of  the 
others  in  this  book,  beginning  with  the  Special  Apparatus,  and 
finishing  with  detailed  Procedure,  giving  step  by  step  instructions 
for  making  this  kind  of  tools.  Show  how  the  proper  hardening 
and  toughening  temperatures  are  to  be  found. 

b.  When  is  it  necessary  to  anneal  a  tool  after  forging? 

c.  If  either  of  two  analyses  would  prove  satisfactory  for  a 
tool,  but  one  required  a  toughening  treatment  some  200°  C. 
higher  than  the  other,  which  steel  should  be  used?     Give  cogent 
reasons. 

d.  Is  it  better  to  quench  and  temper  moderately,  or  to  quench 
the  same  steel  quickly,  and  temper  at  a  higher  heat,  to  give  equal 
hardness?    Why? 

e.  Outline  a  heat  treatment  for  a  sledge  which  would  provide 
a  very  hard  face,  underlain  by  a  tough  body. 


EXPERIMENT  NO.  22 
METALLOGRAPHY  OF  STEELS 

Object.  The  object  of  this  experiment  is  to  produce,  examine, 
and  test  the  various  metarals  existing  in  hardened  and  annealed 
steels. 

General  Explanation.  An  excellent  paper  giving  notes  on 
the  historical  development  of  metallography  has  been  written 
by  Bradley  S  tough  ton,  and  was  published  as  "  Notes  on  the 
Metallography  of  Steel,"  in  Vol.  LIV,  Part  E,  Transactions  of 
the  American  Society  of  Civil  Engineers,  pages  357-421. 

The  names,  production  and  appearances  in  eutectoid  steel  of 
the  various  decomposition  products  ranging  from  austenite  to 
pear  lite  have  been  given  in  former  experiments.  It  should  be 
borne  in  mind  that  the  structure,  as  illustrated,  is  that  developed 
by  proper  etching  agents,  as  a  freshly  polished  piece  of  steel 
appears  brightly  mirrored  at  all  parts,  unless  it  is  a  very  poor 
piece  of  material,  containing  blowholes,  or  specks  of  slag.  It 
is  only  natural  that  different  etching  agents  should  attack  the 
constituents  in  various  manners  and  rates.  The  reagent  in 
universal  use  for  steels  is  an  alcoholic  solution  of  picric  acid, 
made  up  of 

Picric  acid  crystals 5  gm. 

Absolute  alcohol 100  cu.cm. 

Fay  ("  Microscopic  Examination  of  Steel,"  page  17)  recom- 
mends nitric  acid  as  being  superior  to  picric  acid  for  use  on 
hardened  steels.  He  uses  the  following  solution: 

Nitric  acid,  sp.gr.  1.42 4  cu.cm. 

Absolute  alcohol 96  cu.cm. 

167 


168  EXPERIMENTAL  GROUP  IV 

It  is  impossible  to  distinguish  excess  cementite  from  excess 
ferrite  by  these  reagents,  as  both  of  them  attack  massive  crystals 
but  slowly.  If  the  specimen  is  boiled  for  five  to  ten  minutes  in  a 
solution  of  sodium  picrate,  cementite  will  be  colored  black.  The 
reagent  is  made  up  by  dissolving  250  gm.  sodium  hydrate 
(NaOH)  in  750  cu.cm.  of  water,  and  then  dissolving  15  gm. 
picric  acid  crystals  in  the  solution. 

It  will,  perhaps,  be  well  to  recapitulate  and  amplify  somewhat 
the  data  already  presented  on  steel  metarals,  in  order  that  the 


FIG.  30. — Patch  of  Austenite  from  Eutectoid  Steel.      200  X.     Quenched  from 
800°  C.  in  Iced  Brine. 

student  may  recognize  the  entities  he  views  in  the  microscopic 
field. 

Austenite  has  been  defined  as  a  solid  solution  of  cementite 
(FesC)  in  gamma  iron.  It  is  stable  at  various  temperatures 
dependent  upon  its  carbon  content,  which  may  be  any  amount 
up  to  the  saturated  solution  containing  1.7  per  cent.  Austenite 
is  not  nearly  as  hard  as  martensite,  owing  to  its  content  of  the 
soft  gamma  iron.  In  picric  acid,  it  etches  slowly  and  irregu- 
larly— sometimes  faster  and  sometimes  slower  than  martensite, 
and  will  at  various  times  appear  the  darker  or  the  lighter  of  the 
two.  Fig.  30  (reproduced  above)  shows  austenite  to  possess  the 


METALLOGRAPHY  OF  STEELS  169 

typical  appearance  of  any  pure,  crystallized  substance,  cut  at  an 
angle  to  its  cleavage.  Altho  none  of  the  large  crystal  bound- 
aries appear  in  the  field,  the  long-continued  action  of  the  etching 
acid  has  been  to  dissolve  small  particles  from  the  corners  of  the 
regularly  oriented  small  particles  called  crystallites,  which 
together  make  up  the  larger  crystal.  Hence  the  lace-like 
regularity  of  the  markings. 

In  the  most  quickly  quenched  high  carbon  steels,  austenite 
commonly  forms  the  ground  mass  which  is  interspersed  with 


FIG.  31. — Patch  of  Martensite  from  Eutectoid  Steel.     200 X.     Quenched  from 
800°  C.  in  Iced  Brine. 

martensite,  a  large  field  of  which  is  illustrated  in  Fig.  31  (repro- 
duced above).  Martensite  is  usually  considered  to  be  a  solid 
solution  of  cementite  in  beta  iron.  It  is  not  in  equilibrium  in 
any  part  of  the  diagram,  but  represents  an  unstable  condition 
in  which  the  metal  is  caught  during  rapid  cooling.  It  is  very 
hard,  due  to  its  content  of  the  hard  beta  modification,  and  is  the 
chief  constituent  of  hardened  high-carbon  steels,  and  of  medium- 
carbon  nickel-steel  and  manganese-steel.  In  picric  acid,  it 
usually  etches  lighter  than  austenite,  and  always  lighter  than 
troostite.  The  structure  of  uniform  martensite,  as  shown  in 
Fig.  31,  after  six  minutes  etching  in  picric  acid,  has  the  char- 


170 


EXPERIMENTAL  GROUP  IV 


FIG.  32. — Martensite  (light  areas)  pass- 
ing into  Troosite  (dark  areas) .  200  X . 
Eutectoid  Steel,  Quenched  from 
800°  C.,  tempered  at  275°  C. 


FIG.  33. — Martensite  (light  needles; 
passing  into  Troosite  (dark  patches) . 
i3oX.  From  a  piece  of  Eutectoid 
Steel  Electrically  Welded. 


FIG.  34. — Sorbite  (dark  patches)  pass- 
ing into  Pearlite  (wavy  striations). 
Light  Areas  are  Patches  of  Ferrite. 
22oX.  From  a  piece  of  Hypoeutec- 
toid  Steel  Electrically  Welded. 


FIG.  35.*— Carbon  Steel,  i.oo  per 
cent  Carbon.  i5ooX.  Osmond. 
Pearlite,  laminated,  passing  into 
sorbite,  dark  and  formless. 

*  Reproduced  by  permission  from  Saveur, 
"  Metallography  and  Heat  Treatment  of 
Iron  and  Steel." 


METALLOGRAPHY  OF  STEELS  171 

acteristics  of  a  pure  substance,  with  the  etching  lines  developed 
along  an  octahedral  cleavage,  appearing  roughly  parallel  to  the 
sides  of  an  equilateral  triangle.  Indeed,  the  characteristic 
appearance  of  martensite  in  a  field  comprised  of  various  metarals 
consists  of  these  needles,  more  or  less  plainly  marked,  and  inter- 
secting at  an  angle  of  60°,  such  as  is  shown  in  Fig.  33  (see 
page  170). 

Troostite  is  a  metaral  of  doubtful  composition,  but  possibly 
is  an  unstable  mixture  of  untransformed  martensite  with  sorbite 
(q.  v.).  It  contains  more  or  less  untransformed  material,  as  it 
is  too  hard  to  be  composed  entirely  of  the  soft  alpha  modification, 
and  it  can  also  be  tempered  more  or  less  without  changing  in 
appearance.  It  etches  most  rapidly — a  few  seconds  in  picric 
acid  being  all  that  is  required  to  darken  the  area.  Its  normal 
appearance  as  rounded  grains  is  given  in  Fig.  33 ;  larger  patches 
show  practically  no  relief  in  their  structure,  and  a  photo- 
graph merely  shows  a  dark,  structureless  area.  (See  Fig.  32, 
page  170.) 

Sorbite  is  believed  to  be  an  early  stage  in  the  formation  of 
pearlite,  when  the  iron  and  iron  carbide  originally  constituting 
the  solid  solution  (austenite)  have  had  an  opportunity  to  separate 
from  each  other,  and  the  iron  has  entirely  passed  into  the  alpha 
modification,  but  the  particles  are  yet  too  small  to  be  distinguish- 
able under  the  microscope.  It  also,  possibly,  contains  some 
incompletely  transformed  matter.  Sorbite  is  softer,  tougher, 
and  etches  less  quickly  than  troostite,  and  is  habitually  asso- 
ciated with  pearlite.  As  sorbite  is  merely  a  mode  of  aggregation, 
it  has  no  place  on  the  equilibrium  diagram.  Its  components 
are  tending  to  coagulate  into  pearlite,  and  will  do  so  in  a  fairly 
short  time  at  temperatures  near  Aci,  which  heat  will  furnish 
the  necessary  molecular  freedom.  The  normal  appearance  of 
the  substance,  however,  is  the  cloudy  mass  shown  in  Fig.  34 
(page  170),  where  the  metaral  has  been  partially  transformed 
into  the  stable  pearlite. 

Pearlite  is  a  definite  conglomerate  of  ferrite  and  cementite 
containing  about  six  parts  of  the  former  to  one  of  the  latter. 


172  EXPERIMENTAL  GROUP  IV 

When  pure,  it  has  a  carbon  content  of  about  0.95  per  cent. 
It  represents  the  complete  transformation  of  the  eutectoid 
austenite  accomplished  by  slow-cooling  of  an  iron-carbon  alloy 
thru  the  transformation  range.  If  the  steel  is  held  at  tem- 
peratures just  below  Aci  for  some  time,  the  thin  laminations  of 
cementite  agglomerate  into  fine  globules  held  in  a  matrix  of 
ferrite.  This  appearance  is  called  "  granular  pearlite,"  or 
"  spheroidal  cementite."  This  condition,  which  is  shown  in 
Fig.  36,  seems  to  be  a  more  stable  form  of  aggregation  than  the 


FIG.  36. — Spheroidal  Cementite,  or  Granular  Pearlite.     From  a  Piece  of  Eutectoid 

Tool  Steel. 


familiar  lamellar  aggregate  usually  called  pearlite,   and  illus- 
trated in  Fig.  34,  page  170. 

The  micrographs  thus  far  shown  have  been  made  from  eutec- 
toid steels  whose  total  mass  could  resolve  itself  into  pearlite  if  the 
opportunity  presented.  Under  the  microscope,  a  slowly  cooled, 
lower  carbon  steel  shows  more  or  less  primary  ferrite, — soft, 
white  areas  of  alpha  iron — precipitated  from  the  cooling,  under- 
saturated  austenite.  The  balance  of  the  field  consists  of  darker 
patches  of  pearlite, — material  of  eutectoid  composition  and 
constitution.  Fig.  37  shows  a  coarse-grained,  medium-carbon 
steel  magnified  sufficiently  to  show  the  structure  of  the  dark 


METALLOGRAPHY  OF  STEELS 


173 


etching  eutectoid  areas.  The  pearlitic  patches  seldom  have 
developed  striations,  however,  usually  seeming  to  be  merely 
the  dark,  formless  areas  shown  in  Figs.  38  and  39.  This  pair 
of  photographs,  it  may  be  mentioned  in  passing,  is  an  excel- 
lent example  of  the  utility  of  the  microscope  for  determining  the 
condition  of  the  component  crystals  of  a  metal — a  thing  entirely 
beyond  the  province  of  analytical 
chemistry. 

In  a  similar  way,  hyper-eutectoid 
steels,  if  cooled  slowly,  will  show 
bright  primary  cementite  crystals 
bordering  the  dark  pearlitic  areas. 
As  is  also  the  case  with  lower  car- 
bon steels,  various  quenching  and 
annealing  practices  will  suppress  the 
precipitation  of  the  excess  material, 
and  retain  the  whole  mass  in  the 
various  unstable  forms  noted  and 
illustrated  above.  Primary  cemen- 
tite crystals,  as  shown  in  Figs.  40 
and  41,  by  Mr.  E.  P.  Stenger,  need 
not  be  confused  with  excess  ferrite. 
The  experienced  eye  recognizes  a 
marked  difference  in  the  " habit" 
(compare  Figs.  37,  40  and  41).  A 

needle  will  scratch  ferrite  deeply,  but  leave  cementite  untouched. 
Lastly,  sodium  picrate  will  reverse  the  coloration  given  cemen- 
tite by  picric  or  nitric  acid. 

The  preparation  of  specimens  for  microscopic  examination 
has  been  described  in  Experiment  No.  n,  and  the  general  instruc- 
tions need  little  addition.  A  portable  motor  with  vertical  shaft 
carrying  a  round  plate  (Fig.  42,  page  175),  has  been  found  to  be  a 
suitable,  convenient  and  inexpensive  device.  The  coarse  grind- 
ing is  done  by  thin  emery  wheel  disks  of  decreasing  coarseness 
laid  on  the  horizontal  plate.  These  are  followed  by  cloth-covered 
disks,  carrying  finer  and  finer  abrasives,  and  the  specimen  fin- 


FIG.  37. — Medium  Carbon  Steel. 

220X. 


174 


EXPERIMENTAL   GROUP  IV 


ished  on  a  broadcloth-covered  disk  with  rouge   or   levigated 
alumina. 

The  beginner  should  be  very  careful  to  wash  the  specimen 


FIG.  38.— Low  Carbon  Boiler  Plate. 
As  Rolled.     X4o. 


FIG.  39. — Same  as  Fig.  38.     X40. 
From  a  Cold  Flanged  Corner. 


FIG.  40. — High  Carbon  Ingot.     X75- 


FIG.  41. — High  Carbon  Muff  on  Case- 
carburized  Disk.    X 100.    C  =  i  .40%. 


and  his  hands  after  removing  one  disk  and  before  touching  its 
successor.  Disks,  when  not  in  use,  should  be  kept  dust-free  and 
moist  in  a  compression  top  can,  or  under  a  bell  jar. 

Polished  specimens  should  be  kept  in  a  desiccator  over  night 


METALLOGRAPHY  OF  STEELS 


175 


until  their  examination  is  entirely  completed.  At  that  time, 
they  should  be  stored  in  a  fairly  tight  drawer,  enclosed  in  small 
pasteboard  pill  boxes,  wrapped  in  tissue.  In  this  condition, 
they  will  remain  for  years  with  no  appreciable  rusting. 


FIG.  42, — Portable  Grinding  Machine. 

Special   Apparatus.     The    special    apparatus   needed   is   as 
follows : 

Five-gallon  pail  for  quenching  bath. 
Four-inch  watch  glass. 
Nichrome-tipped  forceps. 
Warm  air  blower. 
Soft  hand  towel. 

Supplies.     The  supplies  needed  are  as  follows: 

One  piece  f-in.  eutectoid  steel,  4  in.  long. 

Fragments  of  eutectoid  steel  from  Experiments  Nos.  19 

and  20. 
Six  tension  test  bars  of  4-in.  eutectoid  steel,  machined. 


176  EXPERIMENTAL  GROUP  IV 

Metallography  Room  Equipment.  The  metallography  equip- 
ment needed  is  as  follows: 

Electric  butt  welder. 

Ice. 

Salt. 

Emery  wheel. 

Polishing  machine,  including 

Motor, 

Two  fine  emery  wheels, 

Three  canvas-covered  disks, 

One  broadcloth-covered  disk, 

Four  bell  jars, 

Four  corked  Erlenmeyer  flasks  with  suitable  abrasive. 
Etching  solutions  of  picric  and  nitric  acid. 
Microscopic  set,  including 

Brass  mounting  cup, 

Can  of  BB  lead  shot, 

Cover  glass, 

Candle  lamp  with  condensing  lens  complete. 
Metallographic  microscopic  set,  with 

Plane  glass  reflector, 

Oculars,  5x,  lox, 

Objectives,  8  mm.,  16  mm. 
Scleroscope. 

Procedure,  a.  Clamp  the  bar  of  f-inch  eutectoid  steel 
in  the  jaws  of  the  electric  welder,  as  directed  by  the  instructor. 
Arrange  a  quenching  bath  of  iced  brine  directly  in  front  of  the 
machine.  Turn  on  the  electric  current,  and  when  the  steel 
between  the  jaws  of  the  welder  becomes  white  hot  and  plastic, 
move  the  jaws  slowly  together.  Then  quickly  interrupt  the 
current,  release  the  jaw  grips,  and  drop  the  hot  bar  into  the 
quenching  bath. 

b.  Saw  off  that  portion  of  the  steel  bar  which  was  enclosed  in 
the  welding  machine  grips,  and  grind  a  flat  surface  J  in.  wide  on 


METALLOGRAPHY  OF  STEELS  177 

the  side  of  the  cylinder  remaining.     Grind  slowly  on  a  wet  stone, 
being  very  careful  to  keep  the  ground  surface  cold  at  all  times. 

c.  Prepare  this  surface  on  the  polishing  machine  according  to 
procedures  d  and  e  of  Experiment  No.  n,  page  82,  noting  par- 
ticularly  the   precautions   regarding   cleanliness   mentioned   in 
the  General  Explanation,  above.     Mount  the  specimen  under 
the  microscope  as  in  procedures/  and  g,  Experiment  No.  n,  to 
judge  the  excellence  of  the  polishing,  and  to  examine  for  blow- 
holes or  slag  specks. 

d.  This  specimen  will  show  austenite  at  the  center  of  the  weld, 
and  definite  zones  of  martensite,  troostite,  and  sorbite,  leading 
into  the  unaffected  stock.     Place  a  few  cubic  centimeters  of  the 
alcoholic  nitric  acid  solution  in  a  watch  glass,  and  immerse  the 
polished   surface   for   five   seconds.     Hold   the   specimen   with 
forceps  and  wash  quickly  in  running  water,  shake  off  excess,  dab 
(not  rub)  lightly  with  a  soft  towel,  and  dry  with  a  warm  air  blast. 
Examine  the  piece  carefully  under  the  microscope.     When  the 
band  of  troostite,  which  will  develop  first,  is  definitely  shown, 
exhibit  the  work  to   the  instructor.     Photograph  the  area,  if 
required  by  the  instructor,  following  the  methods  of  Experiment 
No.  12. 

e.  Continue  the  process  by  etching  and  examining  until  the 
entire  surface  has  been  developed  to  a  point  where  the  various 
components  have  singly  been  sharply  exhibited  and  carefully 
examined. 

/.  Explore  the  whole  surface  with  a  scleroscope. 

g.  Procure  the  fragment  of  eutectoid  steel  resulting  from  pro- 
cedure /,  Experiment  No.  19.  Polish,  etch,  and  examine  the 
broken  end,  to  determine  the  constitution. 

h.  Polish,  etch,  and  examine  the  broken  ends  of  all  the 
eutectoid  bars  from  Experiment  No.  20,  obtained  after  all 
reheatings  up  to  A  c  1  +  25. 

i.  From  the  above  work,  decide  upon  the  heat  treatments 
which  will  probably  produce  bars  entirely  of  austenite,  marten- 
site,  troostite,  sorbite,  pearlite,  and  coagulated  cementite.  Pre- 
pare an  outline  of  the  necessary  procedure  to  produce  these  test 


178  EXPERIMENTAL  GROUP  IV 

bars,  and  submit  it  to  the  instructor  for  O.K.  Make  up  a 
complete  list  of  all  the  special  apparatus  and  supplies  needed,  and 
draw  them  from  the  stock-room,  leaving  the  signed  list  as  a 
receipt.  Prepare  the  test  bars,  polishing  and  examining  the  end 
of  each  bar  to  determine  whether  it  has  responded  to  heat  treat- 
ment as  predicted. 

j.  Test  these  bars  in  the  tension  machine  in  the  testing 
laboratory,  either  drawing  a  stress-strain  curve  autographically, 
or  observing  the  necessary  elongations  with  an  extensometer. 
Determine  also  the  hardness  and  impact  strength  of  each  bar- 
end. 

Queries,  a.  Sketch  the  appearance  of  the  polished  and  etched 
weld,  with  proper  notations  recording  the  variations  in  hardness. 

b.  Make  up  a  neat  tabulation  of  all  the  metarals  of  steels, 
showing  the  following  properties  of  each,  as  far  as  determined  or 
known : 

Metaral. 

Equilibrium  range. 

Constitution. 

Composition. 

Etching  characteristics. 

Microscopic  appearance. 

Physical  properties: 

Hardness, 

Elastic  limit, 

Ultimate  strength, 

Elongation. 
Mode  of  production  in  small  pieces  of  eutectoid  steel 

On  quenching, 

On  annealing  or  tempering. 

c.  Figure  the  composition  of  pearlite,  in  percentage  of  ferrite 
and  cementite. 

d.  Why  does  a  steel  containing  0.95—0.50  per  cent  carbon 
show  a  larger  area  of  primary  crystals  than  does  another  con- 
taining 0.95+0.50  per  cent  carbon? 


METALLOGRAPHY  OF  STEELS  179 

e.  Why  should  an  eutectic  structure  be  fine  grained? 
/.  Double  quenching  is  sometimes  used  in  coarsely  crystalline 
bars  to  raise  the  elastic  limit  and  tensile  strength.  Outline  a 
heat  treatment  program  by  which  the  same  result  could  be 
effected  without  the  danger  of  hardening  cracks,  which  would 
almost  assuredly  appear  on  double  quenching  in  any  but  low  or 
medium  carbon  steels. 

g.  Give  a  full  explanation  of  the  changes  which  take  place  in 
pieces  of  carbon  steels  of  the  following  composition  during  heating 
and  cooling: 

0.03  per  cent  carbon. 

0.60 

°-95 

1. 10 


EXPERIMENT  NO.  23 
CASE-CARBURIZING 

Object.  The  object  of  this  experiment  is  to  study  the  cemen- 
tation of  a  mild  steel  bar. 

General  Explanation.*  "  Cementation  processes  "  include 
those  which  enrich  the  surface  of  wrought  iron  or  low-carbon 
steel  to  various  depths  by  the  addition  of  cementite  (FesC). 
The  method  consists  of  heating  a  carbonaceous  substance  in 
close  contact  with  the  iron  to  be  carburized,  in  a  suitable  con- 
tainer. From  the  iron-carbon  equilibrium  diagram,  it  is  evident 
that  Ac i  is  the  minimum  temperature  at  which  true  cementation 
can  proceed;  graphitic  carbon  will  diffuse  into  iron  at  lower  tem- 
peratures than  this  by  reason  of  the  forces  due  to  a  difference  in 
concentration,  and  if  it  does  combine  with  the  iron,  the  carbide 
produced  cannot  enter  into  solid  solution  until  Ac\  is  exceeded. 
Otherwise  the  properties  of  a  more  highly  carburized  steel  are 
lacking — the  added  cementite  does  not  form  increasingly  large 
areas  of  pearlite,  but  remains  as  a  fine  meshwork  of  free  crystals 
wherever  formed. 

Apparently,  the  most  obvious  variation  in  cemented  metal  is 
the  depth  to  which  the  carburization  extends.  On  this  basis 
has  grown  a  distinction  between  "  total  "  cementation,  where  the 
piece  is  intended  to  be  wholly  transformed  into  a  high-carbon 
steel,  and  "  partial  "  cementation,  where  the  process  is  frankly 
limited  to  the  production  of  a  thin,  hard  case  overlying  the  orig- 
inal low-carbon,  tough  material.  As  a  matter  of  fact,  the  term 

*  This  explanation  is  condensed  from  a  longer  article  by  the  author  appear- 
ing in  XVI,  "Metallurgical  and  Chemical  Engineering,"  385.  The  great  au- 
thority, on  the  matter  of  case-carburizing  is  Giolitti,  "  The  Cementation  of  Iron 
and  Steel." 

180 


CASE-CARBURIZING  181 

"  total  cementation  "  is  a  misnomer,  inasmuch  as  the  process  is 
seldom  if  ever  continued  for  a  time  when  there  is  a  considerable 
increase  in  the  carbon  content  at  the  very  center  of  the  metal. 

A  description  of  the  methods  of  cementation  for  the  produc- 
tion of  blister  steel  is  beside  the  scope  of  the  present  discussion, 
and  the  student  is  referred  to  the  article  noted  above,  or  to  Mills, 
"  Materials  of  Construction,"  pages  363  to  365. 

Altho  the  manufacture  of  blister  steel  may  be  on  the  decline, 
the  advances  in  machine  design  call  for  an  increasingly  large 
number  of  parts  which  are  hard  enough  to  resist  wear,  but  are 
tough  enough  to  withstand  shocks.  It  is  well  known  that  a 
high  hardness  numeral  is  had  at  the  expense  of  ductility,  but  the 
combination  of  these  desirable  but  contradictory  qualities  may 
happily  be  had  by  transforming  the  outer  surface  of  a  tough,  low- 
carbon  piece  into  a  hard,  high-carbon  steel.  Again,  case- 
hardening  operations  are  the  favorite  method  for  producing  cheap 
metallic  pieces  for  taking  a  high  polish.  Or,  lastly,  the  ends  of 
such  articles  as  axles  may  be  carburized  for  the  wear  against 
bearings,  while  the  rest  of  the  bar  can  be  entirely  unaltered. 

The  methods  for  this  most  important  operation  of  case-car- 
burization  are  various,  depending  first  of  all  upon  the  cement 
used,  whether  solid,  liquid  or  gaseous,  or  some  combination  of 
these  three.  As  a  matter  of  fact,  most  case-carburization  is  still 
done  by  packing  the  pieces  in  crushed  charcoal  or  other  car- 
bonaceous material  in  closed  metallic  boxes,  and  then  heating  the 
combination  to  a  proper  degree,  and  for  a  proper  time. 

A  superficial  consideration  would  suggest  that  the  carbur- 
izing  action  is  due  to  the  diffusion  of  the  solid  carbon  of  the 
cement  into  the  carbon-poor  iron.  Doubt  is  thrown  upon  this 
view  when  it  is  known  that  charcoal,  as  a  cement,  is  rapidly 
"  exhausted  ";  that  is  to  say,  its  efficiency  is  continuously  im- 
paired upon  re-use.  Careful  experimenting  has  shown  that 
actual  physical  contact  of  the  iron  and  carbon  is  the  prime  requisite 
of  solid  diffusion.  When  this  requirement  is  rigorously  met,  a 
three  and  one-half  hour  cementation  in  pulverized  carbon  at 
1000°  C.  will  increase  the  pearlitic  areas  very  slightly  to  a  depth 


182  EXPERIMENTAL   GROUP  IV 

of  0.15  mm.,  while  any  portion  more  than  this  distance  from  a 
carbon  contact  will  be  absolutely  unaltered.  Evidently  the 
deeper  carbonized  layers  so  easily  produced  in  practice  must  be 
explained  in  some  other  way. 

Without  dwelling  at  length  upon  the  various  other  possibili- 
ties, we  may  accept  it  as  definitely  proven  that  carbon  monoxide 
(CO)  is  the  most  active  cementing  material  existing  in  the 
ordinary  carbonizing  box,  and  fortunately  the  most  easily  con- 
trolled. 

Interaction  between  the  oxygen  of  the  air  occluded  in  the 
charcoal  pores  and  entrapped  in  the  cementation  box  with  the 
heated  carbon  produces  quantities  of  carbon  dioxide  (CO2)  at 
low  temperatures.  At  the  temperature  of  ordinary  cementation 
—  over  1000°  C.  —  most  of  the  carbon  dioxide  gas  decomposes, 
if  in  contact  with  an  excess  of  carbon,  forming  carbon  monoxide 
(CO).  This  is  indicated  by  the  reversible  reaction 


The  resulting  gas  has  a  very  small  proportion  of  carbon  dioxide, 
the  actual  amounts  of  each  gas  in  equilibrium  varying  with  the 
temperature  and  pressure.  These  conditions  of  equilibrium  may 
be  noted,  in  a  short-hand  way,  by  saying  that  there  exists  an 
equilibrium  in  the  system  C  :  CO  :  C02.  The  gas  resulting 
from  this  equilibrium,  particularly  the  carbon  monoxide,  easily 
diffuses  into  the  hot  iron  and  reacts  with  it,  forming  iron  car- 
bide, which  is  immediately  absorbed  into  the  solid  solution 
austenite.  The  reaction  may  be 


The  dioxide  formed  at  this  point  diffuses  outward  to  a  region 
of  lower  concentration,  while  the  CO  :  CO2  diffusing  inward  will 
form  more  iron  carbide  on  its  way  to  the  center  of  the  piece  of 
metal  if  demanded  by  the  state  of  the  system,  Austenite: 
CO  :  CO2,  existing  at  that  particular  locality.  The  carbon 
dioxide  escaping  from  the  steel  is  immediately  regenerated  by 


CASE-CARBURIZING  183 

the  excess  of  hot  carbon  to  a  condition  represented  by  the  equilib- 
rium of  the  system  C  :  CO  :  CO2- 

It  is  clearly  seen  that  carburization  will  cease  when  the 
relative  concentration  of  the  gases  in  the  packing  represented  by 
C  :  CO  :  CO2  equals  that  existing  in  the  steel,  which  is  repre- 
sented by  Austenite  :  CO  :  C02-  As  a  matter  of  fact  the 
maximum  carbon  concentration  in  a  case-hardened  article 
never  reaches  this  theoretical  amount,  simply  because  the  proc- 
ess is  interrupted  long  before  equilibrium  is  established. 

Of  all  the  solid  cements,  wood  charcoal  is  the  best;  first, 
because  it  is  pure,  and  therefore  maintains  the  purity  of  the 
product;  and  second,  it  is  of  simple  composition,  and  therefore 
the  carburizing  reactions  are  not  complicated  by  variable  and 
unknown  factors.  This  allows  its  use  with  certainty  of  control; 
the  results  can  be  predicted  with  considerable  accuracy.  The 
greatest  disadvantages  are  the  slow  speed  of  the  cement  and  the 
phenomenon  of  "  exhaustion,"  both  of  which  now  seem  to  be  due 
to  the  limited  amount  of  carbon  monoxide  formed  in  the  box. 
In  order  to  increase  the  speed  of  the  cement,  it  is  necessary  to  add 
one-third  to  one-half  unused  charcoal  to  every  packing,  or  better, 
to  mix  into  the  charcoal  in  the  first  place  some  40  per  cent 
of  powdered  witherite  (BaCOs).  The  latter  procedure,  recom- 
mended by  Caron  in  1861,  is  especially  valuable  in  increasing 
the  efficacy  of  the  cement  by  bringing  a  large  amount  of  gas  to 
the  cementation  chamber  in  the  following  manner: 

BaCO3<=±BaO  +  CO2, 


The  first  reaction  goes  toward  the  left  at  lower  temperatures  — 
CO2  being  rapidly  absorbed  upon  exposure  to  the  air.  Such  a 
combination  has  the  added  advantage,  therefore,  of  being  inex- 
haustible; it  is  largely  used  today,  and  all  things  considered,  is 
the  best  solid  cement  for  "  partial  "  cementation. 

Innumerable  preparations  have  been  recommended  and  are 
on  the  market  for  use  as  solid  cements,  but  "  there  are  only  some 
types  of  simple  cements,  at  present  well  known,  whose  efficacy 


184  EXPERIMENTAL  GROUP  IV 

is  a  maximum  from  all  points  of  view,  and  the  addition  of  other 
ingredients  in  no  wise  increase  their  efficacy  "  (Giolitti,  "  The  Ce- 
mentation of  Iron  and  Steel,"  page  261).  Unfortunately, 
Caron's  cement  requires  considerable  time  to  produce  its  deep- 
seated  carbonizations.  More  "  rapid  "  cements  are  made  of 
many  mixtures  of  sawdust,  charcoal,  bone,  lampblack,  tar  and 
various  hydrocarbons,  alkaline  and  alkaline  earth  carbonates  and 
cyanides,  ferro-  and  ferri-cyanides;  together  with  homeopathic 
proportions  of  numberless  other  substances,  all  more  or  less  inert. 

Such  compounds  act  by  virtue  of  the  large  quantities  of  hydro- 
carbons or  cyanides  which  are  evolved  on  heating;  they  exhaust 
rapidly,  give  very  irregular  and  non-uniform  carbon  penetra- 
tions with  a  rapid,  discontinuous  rise  from  the  non-cemented 
core  to  the  thin,  excessively  high-carbon  concentrations  at  the 
outside.  The  variable  quantities  of  complex  gaseous  mixtures 
evolved  in  the  cementation  box  preclude  even  a  moderately 
close  control  of  the  process,  and  result 'in  a  non-uniform  product 
containing  a  hard,  brittle  case  badly  addicted  to  exfoliation. 
In  cementation  as  well  as  other  processes,  the  simplest  combina- 
tions are  managed  with  difficulty,  while  any  such  variable  and 
complex  mixtures  as  are  produced  by  the  destructive  distillation 
of  organic  materials  are  absolutely  uncontrollable. 

The  use  of  a  molten  bath  of  carburizing  materials  presents  a 
great  many  apparent  advantages  as  to  ease  of  manipulation  and 
cheapness  of  product.  The  materials  composing  these  baths 
are  usually  cyanides  or  cyanogen  compounds,  all  highly  poisonous. 
The  chemical  reactions  occurring  in  such  baths  have  not  been 
studied  with  precision,  but  it  seems  that  the  cyanogen  (CN)2 
decomposes  in  contact  with  the  iron  yielding  carbon,  which  is 
absorbed  into  the  surface  layers  of  the  metal.  The  time  of 
cementation  is  so  short,  however,  that  the  carbide  thus  formed 
has  little  chance  to  penetrate  into  the  metal,  and  the  result  is  a 
very  thin  zone  (0.03  to  o.i  mm.)  of  hypereutectoid  steel.  Deeper 
zones  result  in  very  brittle  and  higher  carbon  muffs  which  are 
liable  to  split  off  when  quenched,  i.e.,  "  exfoliate." 

Since  carbon  monoxide  gas  is  the  active  cementation  agent 


CASE-CARBURIZING  185 

even  when  the  so-called  solid  cements  are  used,  it  would  appear 
that  the  best  course  would  be  frankly  to  adopt  this  gas  as  a 
carburizing  agent.  Theoretically,  it  would  seem  that  a  high 
degree  of  uniformity  in  the  case-carburized  bars  could  be  pro- 
duced with  certainty  by  feeding  to  the  container  a  gas  of  the 
proper  composition  (xCO+yCO2)  which,  at  the  temperature  of 
the  furnace,  would  be  in  equilibrium  with  the  system 

*Austenite  :  CO  :  CO2. 

where  x  Austenite  represents  the  per  cent  of  carbon  desired  in  the 
muff.  In  such  a  case,  the  time  element  would  be  absolutely 
powerless  to  increase  the  maximum  carbon  content  of  the  case,  it 
would  only  produce  a  deeper  and  deeper  zone  of  uniform  compo- 
sition. 

Practically,  however,  the  equilibrium  represented  by  #  Austen- 
ite is  approached  in  the  outer  layer  of  the  steel  with  extreme 
slowness,  owing  to  the  counter  effect  of  the  carbon  dioxide  dif- 
fusing from  the  lower  carbon  austenite  at  the  center  of  the  bar 
outward  toward  the  gaseous  atmosphere.  For,  as  the  action  of 
carbon  monoxide  going  inward  is  a  carburization,  for  like  reasons 
a  stream  of  carbon  dioxide  coming  out  will  decarburize.  Even 
so,  the  carbon  content  of  the  finished  bar  carburized  in  carbon 
monoxide  diminishes  from  the  case  inward  with  absolute  uni- 
formity and  even  this  slow  process  would  be  used  where  a  zone 
of  this  characteristic  (called  Type  I  by  Giolitti)  would  be  desir- 
able. 

Cemented  zones  belonging  to  Giolitti 's  Type  II  are  pro- 
duced by  the  use  of  ethylene,  methane,  acetylene,  or  other  hydro- 
carbons which  decompose  at  elevated  temperatures  when  in 
contact  with  iron,  depositing  a  larger  or  smaller  quantity  of  the 
finest  carbon  on  the  outside  of  the  specimen.  The  distinctive 
feature  of  cementations  of  Type  II  is  the  possession  of  a  hyper- 
eutectoid  case,  whereas  Type  I  always  produces  hypoeutectoid 
zones.  In  addition  to  this  characteristic,  a  slowly  cooled  zone 
of  Type  II  shows  the  existence  of  three  distinct  zones  shown 
plainly  in  the  micrograph,  Fig.  43  (reproduced  from  Giolitti, 


c% 

1.4 
1.2 
1.0 
0.8 
O.G 
0.4 
0.2 

"v^— 

>••'••». 

X 



L- 

:v 

\ 

V 

\ 

\ 

0        0.5         1          1.5        2        2.5         3   MM. 

FIG.  44. — Concentration  Depth  Diagram 
of  Bar  Carburized  with  Ethylene. 
5  Hours  at  1050°  C. 

NOTE — Figs.  43  to  46  inclusive  have  been 
reproduced  from  Giolotti.  "  Cementation  of 
Iron  and  Steel,"  by  permission  of  the  McGraw- 
Hill  Book  Co. 


FIG.  43. — Microsection  of  Edge  of 
Bar  Carburized  with  Ethylene. 
5  Hours  at  1050°  C. 


186 


CASE-CARBURIZING  187 

Fig.  38),  and  the  corresponding  concentration-depth  diagram, 
Fig.  44  (reproduced  from  Giolitti,  Fig.  37),  which  were  produced 
by  a  four-hour  cementation  in  ethylene,  at  1050°  C. 

The  mechanism  of  this  action  is  not  quite  clear,  but  it  is 
possible  that  the  hydrocarbons  decompose  so  rapidly  upon 
entering  the  steel  that  a  deposit  of  carbon  is  formed  on  the  out- 
side of  the  steel  much  more  rapidly  than  it  can  diffuse  into  the 
metal.  This  lavish  deposition  of  carbon  evidently  continues  as 
the  gases  penetrate  further,  the  direct  action  of  the  decomposing 
gases  being  intensified  by  the  presence  of  the  excess  of  carbon 
deposited  on  the  surface  of  the  sample  as  well  as  being  possibly 
reinforced  by  the  diffusion  of  the  carbon  bodily  into  the  steel 
(perhaps  a  considerable  factor  in  this  instance  owing  to  the  fine 
subdivision  and  intimate  contact  of  the  sooty  deposit).  For 
these  reasons  a  high  carbon  concentration  is  obtained  with  a  zone 
of  zAustenite  of  considerable  thickness  (i  mm.-|-). 

It  is  therefore  evident  that  the  best  results  (from  a  practical 
standpoint)  may  be  attained  by  a  proper  mixture  of  carbon  mon- 
oxide and  one  of  the  gases  of  Type  II.  These  actually  do  pro- 
duce most  desirable  results,  called  Type  III,  giving  rise  to  car- 
burized  cases  of  varying  thicknesses  approximating  eutectoid 
composition  at  the  exterior,  underlain  by  steel  of  constantly  and 
uniformly  decreasing  carbon  content,  merging  into  the  unaffected 
core.  The  characteristics  of  this  class  of  carburized  zones  are 
illustrated  in  the  micrograph,  Fig.  45  (reproduced  from  Fig. 
142,  Giolitti),  and  the  concentration-depth  diagram,  Fig.  46 
(reproduced  from  Giolitti,  Fig.  45). 

Zones  of  Type  III  are  doubtless  produced  in  the  following 
manner:  The  hydrocarbons  in  contact  with  the  outer  layer  of 
the  iron  decompose,  depositing  free  carbon.  This  carbon  con- 
tinually regenerates  the  CCb  diffusing  outward,  and  the  resulting 
CO  really  acts  as  a  vehicle,  transporting  the  carbon  to  deeper 
and  deeper  regions,  where  it  could  not  possibly  penetrate  by  solid 
diffusion  on  account  of  time  and  temperature  limitations. 

Very  important  advances  have  recently  been  made  in  the 
construction  of  furnaces  for  the  practice  of  cementation  with  solid 


FIG.  45. — Microsection  of  Edge  of  Bar 
Carburized  with  Giolitti's  Mixed 
Cement.  2  Hours  at  1000°  C.  50  X. 


1 

0.8 

0.6 

0.4 

0.2 


0          0.2       0.4       0.6       0.8         1          1.2        1.4        1.6       1.8         ?         2.2       2.4 

FIG.  46. — Concentration  Depth  Diagram  of  Bar  Carburized  with  CO+3.i%C2H4. 

4  Hours  at  1000°  C. 

188 


CASE-CARBURIZING  189 

or  gaseous  cements.  For  a  description  of  these  improved  appa- 
ratus, the  interested  student  will  refer  to  the  works  mentioned 
at  the  head  of  this  general  explanation.  In  comparison  with  the 
old-fashioned  furnaces  which  plant-managers  refuse  to  scrap 
because  they  fail  to  recognize  their  economic  wastefulness,  the 
extraordinary  work  of  these  new  types  may  be  illustrated  by 
saying  that  with  a  gaseous  cement  a  penetration  of  from  0.7  to 
1.2  mm.  may  be  obtained  in  an  hour  with  a  maximum  carbon 
concentration  approaching  0.9  per  cent.  Such  a  case,  by  the 
way,  is  ample  for  99  per  cent  of  all  machine  parts  subjected  to 
partial  carbonization.  Using  properly  designed  furnaces  oper- 
ating with  solid  cements,  from  ten  to  twenty  cementations  can 
be  effected  in  a  day  of  twenty-four  hours,  depending  upon  the 
depth  of  case  required,  turning  out  from  one  to  five  tons  of 
material  per  furnace,  at  a  maximum  cost  of  one  cent  per  pound — 
one-fifth  that  of  carburization  in  boxes. 

A  perplexing  and  most  troublesome  phenomenon  attendant 
upon  the  use  of  cemented  steel  objects  is  the  exfoliation  or  split- 
ting of  the  carburized  zone  from  the  piece  during  quenching,  or  in 
use.  Dr.  Giolitti  shows  that  these  failures  occur  at  points  where 
a  sudden  and  discontinuous  variation  in  the  carbon  content 
occurs  in  the  carburized  zone — as  in  the  case  of  the  middle  zone 
of  cementations  of  Type  II.  The  reasons  why  this  failure  occurs 
at  such  points,  and  how  it  can  be  avoided  have  been  explained 
by  E.  P.  Stenger,  in  an  article  published  in  XVI  "  Metallurgical 
and  Chemical  Engineering,"  424. 

Special  Apparatus.  The  special,  apparatus  needed  is  as  fol- 
lows: 

One  piece  2-in.  gas  pipe,  4  in.  long,  threaded. 

Two  2-in.  pipe  sleeves. 

Two  2-in.  pipe  plugs. 

Breast  drill  and  f-in.  bit.         Monkey  wrench. 

Large  pipe  wrench.  Electrical  meter. 

Special  squads  will  need  a  supply  of  f-in  pipe, 

f-in.  pipe  fittings, 
drum  of  CO. 


190  EXPERIMENTAL  GROUP  IV 

Supplies.     The  supplies  needed  are  as  follows: 

Three  round  f -in.  bars  of  2o-point  carbon  steel,  6  in.  long. 
Can  of  carburizer. 

Laboratory  Equipment.  The  laboratory  equipment  needed 
is  as  follows: 

Pipe  vise. 

Ice. 

Emery  wheel  with  wire  buffing  brush. 

Impact  machine. 

Scleroscope. 

Gas  furnace  at  1000°  C.,  with  temperature  regulator. 

Metallography  Room  Equipment.  The  metallography  room 
equipment  needed  is  as  follows: 

Polishing  machine,  complete  1       ^        .        ,  AT 

. ,.          3  .  \  v.  Experiment  No.  22. 

Microscopic  set,  complete 

Etching  solution  of  picric  or  nitric  acid. 

Procedure,  a.  Make  a  carburizing  box  for  the  f-in.  round 
test  pieces  as  follows:  On  either  end  of  a  piece  of  2-in.  gas  pipe, 
4  in.  long,  screw  a  sleeve,  and  into  the  sleeve  a  plug.  One  of  the 
plugs  should  have  a  f-in.  pyrometer  hole  in  its  center. 

b.  Pack  the  box  by  placing  about  \  in.  of  the  solid  carburizer 
in  the  bottom,  and  then  standing  the  three  test  bars  equidistant 
from  each  other  and  the  walls.     Fill  the  remainder  of  the  box 
with  the  carbonaceous  material,  screw  in  the  top  plug  and  in- 
sert the  asbestos  protected  thermo-couple  (Experiment  No.  7) 
thru  the  pyrometer  hole  well  toward   the  center  of  the  mass. 
Lute  the  hole  shut  with  asbestos  string. 

c.  Place  this  box  in  a  hardening  furnace  held  at  1000°  C. 
with  a  temperature  regulator.     The  temperature  of  the  pieces 
in  the  carburizing  box  should  be  held  at  a  constant  maximum  for 
three  hours.     One  squad  member  should  give  his  entire  time  to 
the  furnace  control,  reading  and  plotting  the  temperature  in  the 
box  and  of  the  furnace  at  short  intervals.     Cool  in  the  furnace. 


CASE-CARBURIZING  19l 

d.  In  the  following  laboratory  period,  open  the  box,  observe 
the  condition  of  the  bars,  and  clean  them  with  a  wire  buffing 
brush.     Break  three  pieces  from  the  end  of  one  bar  in  the  impact 
machine,  according  to  procedure/,  Experiment  No.  17,  taking 
the  average  result  as  the  toughness.     Grind  one  end  of  the  frag- 
ments and  explore  the  area  carefully  for  variations  in  hardness. 
Preserve   one  fragment  to  exhibit  the  coarseness  of  the  frac- 
ture, and  paste  a  label  around  it,  giving  its  properties  and 
history. 

e.  Polish  one  end  of  another  fragment  (procedure  d  and  e, 
Experiment  No.  n),  etch  (procedure  d,  Experiment  No.  22), 
and  examine  under  the  microscope  (procedure  /  and  g,  Experi- 
ment No.  n).     Sketch  the  appearance  of  the  microscopic  field 
according  to  procedure  /,  Experiment    No.    n,  or  photograph. 
With  the  aid  of  the  instructor,  estimate  the  carbon  content  of 
the  case,  and  sketch  an  approximate  concentration-depth  dia- 
gram, like  Fig.  46. 

/.  Refine  the  grain  of  the  two  remaining  pieces  by  annealing 
at  the  proper  temperature,  according  to  Experiment  No.  17. 
Test  one  of  the  annealed  pieces  as  in  procedure  d,  above. 

g.  Harden  the  case  on  the  remaining  piece  by  quenching  in 
oil  from  the  proper  temperature,  according  to  Experiment  No. 
1 8  and  19.  Test  the  piece  as  in  procedure  d,  above. 

h.  Mount  representative  fragments  by  thrusting  them  thru 

.small  holes  in  a  sheet  of  cardboard.     Add  a  tabulation  of  the 

data  and  a  copy  of  the  sketches  and  temperature  curves  obtained 

during  the  experiment.     Post  the  whole  on  the  bulletin  board 

for  examination  by  the  various  squads. 

NOTE. — Each  squad  should  have  individual  instructions  as 
to  time,  temperature,  and  agent  of  cementation.  In  this  way 
the  final  results  can  be  examined  by  all  students,  and  will  exhibit 
how  the  properties  of  case-carburized  bars  vary  with  the  con- 
ditions. A  suggested  program  of  such  variations  is  as  follows: 

I.  To  show  the  effect  of  constancy  of  temperature.  Use 
Caron's  cement. 


192  EXPERIMENTAL  GROUP  IV 

Squad  i.    Heat  three  hours  at  1000°  C.,  in  hand-controlled  oven  furnace. 
Squad  2.     Heat  three  hours  at  1000°  C.,  in  hardening  furnace  equipped 

with  automatic  temperature  control. 

Squad  3.     Heat  three  hours  at  1000°  C.,  in  an  electric  tube  furnace. 
Squad  4.    Heat  three  hours  in  oven  furnace  purposely  oscillating  the 

temperature  from  900  to  1000°  C. 

II.  To  show  the  effect  of  varying  the  carburizing  agent: 
Compare  the  work  of  Squad  2  with 

Squad  5.  Use  crushed  charcoal  only — thru  i^-in.  on  £-in  riddle. 
Squad  6.  Use  the  same  material  after  Squad  5  has  used  it  once. 
Squad  7.  Use  the  same  material  after  Squad  5  and  6.  Connect  a  drum 

of  CO  to  the  carburizing  box  by  a  |-in.  pipe,  and  pass  a  very  slow  stream 

of  gas  at  all  times. 
Squad  8.     Pack  the  bars  in  crushed  charcoal,  connect  a  f-in.  pipe  to  the 

air  supply,  and  pass  a  very  slow  stream  of  air  thru  the  box,  starting 

when  the  bars  have  reached  the  desired  temperature.      A  few  cubic 

centimeters  of  gas  per  minute  is  all  that  is  required. 
Squad  9.     Use  an  inert  substance  like  crushed  silica  brick  for  a  packing 

and  pass  a  slow  stream  of  CO  thru  the  box  at  all  times. 
Squad  10.     Pack  as  Squad  9,  but  use  a  slow  stream  of  natural  gas. 

III.  To  show  the  effect  of  temperature: 
Compare  the  work  of  Squad  2  with 

Squid  ii.  Working  in  exactly  the  same  way  as  Squad  2,  except  at 
800°  C. 

IV.  To  show  the  effect  of  time: 
Compare  the  work  of  Squad  2  with 

Squad  12.  Working  in  exactly  the  same  way  as  Squad  2,  except  that  the 
heating  should  be  continued  only  i  \  hours,  and  the  pieces  taken  from 
the  hot  container  and  cooled  in  air. 

Queries,  a.  Why  is  it  impossible  to  produce  a  bar  of  uni-. 
form  carbon  content  edge  to  center,  by  the  method  of  "  total  " 
cementation? 

b.  If  a  piece  of  wrought  iron  were  exposed  to  a  continual 
stream  of  carbon  monoxide  gas  at  a  temperature    above  Ac\, 
what  would  be  the  ultimate  carbon  content  of  the  bar?     Why? 

c.  Sketch   a  modern  furnace  for  carburization  with  solid 
cement. 

d.  Discuss  the  effect  of  temperature  variation  during  carburi- 
zation on  the  properties  of  the  resulting  bar. 

e.  Discuss  the  effect  of  time  at  the  carburizing  heat  on  the 
properties  of  the  resulting  bar. 


CASE-CARBURIZING  193 

/.  Discuss  the  results  of  carburizing  with  different  agents. 
Why  does  charcoal  exhaust  itself?  Why  does  not  Caron's 
cement  do  likewise?  Explain  the  "  regeneration  "  of  charcoal 
by  a  stream  of  CO  or  air.  Is  the  case  resulting  from  a  carburiza- 
tion  in  natural  gas  a  representative  of  Type  I,  II,  or  III?  Why? 

g.  Describe  the  process  of  manufacture  of  blister  steel. 

h.  Discuss  the  causes  and  remedy  for  exfoliation. 


EXPERIMENT  NO.  24 
CORROSION 

Object.  The  object  of  this  experiment  is  to  study  the  cor- 
rosion of  steel. 

General  Explanation.*  It  is  a  matter  of  universal  experience 
that  dry  metal  does  not  rust.  All  scientific  hypotheses  as  to 
the  nature  of  corrosion  require  the  presence  of  water,  which  we 
will  assume  to  be  the  rain,  surface,  or  ground  water.  All  terres- 
trial water  is  impure,  containing  a  greater  or  less  proportion  of 
other  matter;  that  is  to  say,  it  is  a  "  solution  "  of  organic  and 
inorganic  matter.  It  is  well,  therefore,  first  to  consider  the  prop- 
erties of  solutions. 

If  a  quantity  of  soluble  salt  is  placed  in  pure  water,  it  will 
enter  into  solution  at  a  certain  rate.  The  molecules  of  the  solid 
tend  to  distribute  themselves  among  the  molecules  of  the  liquid 
equi-spatially.  The  speed  of  solution  progressively  diminishes 
owing  to  a  back-pressure  called  "  osmotic  pressure  "  exerted  by 
the  molecules  which  have  gone  into  solution,  until  when  the  sat- 
uration point  is  reached  the  solution  pressure  is  exactly  balanced 
by  the  osmotic  pressure,  and  any  molecules  which  may  go  into 
solution  will  be  replaced  by  others  coming  out  of  solution.  The 
system  is  one  of  balanced  activity,  or  equilibrium. 

Arrhenius  first  pointed  out  the  fact  that  the  molecule?  of 
inorganic  salts,  acids,  or  bases  in  aqueous  solution  are  dissociated 
when  entering  into  a  solution.  The  main  arguments  for  this 
theory  were  drawn  from  a  study  of  osmotic  pressure. 

Osmotic  pressure  may  be  measured  by  suitable  apparatus, 
and  for  an  organic  solution,  such  as  sugar  in  water,  it  has  been 

*  The  best  authority  on  corrosion  is  Cushman  and  Gardner,  "  The  Corrosion 
and  Preservation  of  Iron  and  Steel." 

194 


CORROSION  195 

found  to  obey  the  gas  laws.  In  other  words,  osmotic  pressure 
varies  as  the  absolute  temperature,  and  as  the  concentration  of 
molecules;  in  fact,  the  osmotic  pressure  is  exactly  equal  to  the 
pressure  it  would  exert -were  the  substance  a  gas  at  the  same 
volume  and  temperature.  Inorganic  substances,  however,  ex- 
hibit an  osmotic  pressure  two,  three,  or  four  times  as  much  as 
the  same  molecular  concentration  of  organic  substances.  Again, 
if  a  certain  concentration  of  sugar  depresses  the  freezing-point 
or  the  vapor  pressure  of  a  solution  an  amount  equal  to  one  unit, 
the  same  molecular  concentration  of  salt  (NaCl)  will  depress 
it  two  units;  while  barium  chloride  (BaCk)  will  depress  it  three 
units. 

These  various  facts  were  explained  by  Arrhenius  by  the 
assumption  that  the  sugar  molecule  enters  the  solution  as  such, 
but  that  salt  enters  as  two  distinct  particles  (Na)  and  (Cl), 
while  BaCl2  enters  as  three:  (Ba),  (Cl),  and  (Cl). 

It  is  unquestionably  true  that  the  dissociated  parts  of  an 
inorganic  salt  are  in  some  manner  different  from  elemental 
matter.  In  the  case  of  common  salt  fNaCl)  the  sodium  is  not 
in  the  atomic  state,  else  it  would  violently  attack  water,  liberat- 
ing hydrogen,  while  atomic  chlorine  would  color  the  solution 
and  give  a  characteristic  odor.  None  of  these  things  happen 
when  salt  goes  into  solution.  This  has  been  explained  by  the 
theory  that  the  instant  the  molecule  of  salt  dissociates,  the 
particles  become  "  ionized."  That  is  to  say,  the  sodium  (which 
is  possibly  only  a  definite  aggregate  of  minute  electrical  par- 
ticles of  high  intrinsic  energy  but  small  mass  called  "  electrons  ") 
is  no  longer  an  atom  but  an  "  ion  "  because  it  contains  one  too 
many  electrons,  and  the  chlorine  is  no  longer  atomic  but  ionic 
because  it  lacks  the  one  electron  attached  to  the  sodium.  The 
sodium  is  thus  charged  positively,  while  the  chlorine  is  charged 
negatively.  Due  to  the  attraction  of  the  unlike  charges  the 
sodium  and  chlorine  ions  are  continually  recombining,  but  also 
continually  dissociating — the  system  again  being  one  of  bal- 
anced activity  or  equilibrium. 

A  directional  impetus  could  evidently  be  given  these  wander- 


196 


EXPERIMENTAL   GROUP  IV 


ing  ions  by  immersing  a  pair  of  places  into  a  dissociated  solution 
and  maintaining  a  positive  charge  on  the  one  and  a  negative 
charge  on  the  other.  The  first  would  attract  the  negatively 
charged  ion,  and  vice  versa.  This  experiment  is  easily  per- 
formed with  apparatus  as  shown  in  Fig.  47. 

The  battery  sends  a  constant  supply  of  positive  particles  of 
electricity  to  the  copper  plate,  and  an  equal  supply  of  negative 
particles  to  the  iron.  In  solution,  the  molecules  of  sulfuric  acid 
(H2SO4)  are  dissociated  into  three  ions  which  may  be  noted. 

(H)+   (H)+   (S04)~. 

The  hydrogen  ions,  positively  charged  and  free  to  move,  will 
be  pulled  toward  the  iron  plate  and  pushed  away  from  the  copper 


4-  Wire 


6  Volt 
Battery 


Cu 

/^ 

, 

AAA/  Resistance              —  1  — 

Fe 

-Wire 

f 

-*-Beaker  with 
Ifc  Ho  SO  4  Solution 

^D-J 

FIG.  47. — Electrolysis  of  Inorganic  Solutions. 

plate,  and  will  continuously  come  into  contact  with  the  negative 
iron  electrode.  For  similar  reasons  we  expect  the  (SCU)""  ions 
to  simultaneously  reach  the  positive  copper  electrode.  As  soon 
as  the  hydrogen  ion  touches  the  anode,  a  certain  amount  of 
electricity  is  neutralized,  and  the  hydrogen  now  becomes  atomic, 
unites  with  a  second  atom,  forming  molecules  of  hydrogen  gas, 
which  gather  in  bubbles  on  the  surface  of  the  metal  and  escape 
from  the  solution. 

The  (864)  ion,  on  coming  into  contact  with  the  electrode, 
and  losing  its  electrical  charge  becomes  a  chemical  entity  of 
extreme  activity,  attacking  the  metal  with  which  it  is  in  contact 
forming  copper  sulfate,  CuSO4,  which  being  soluble,  enters 


CORROSION 


197 


the  solution  and  immediately  dissociates.  The  presence  of 
copper  in  the  solution  is  quickly  detected  by  the  characteristic 
blue  color  in  the  vicinity  of  the  cathode. 

The  migration  of  the  ions  in  this  case  involves  the  neutraliza- 
tion of  a  considerable  quantity  of  electricity  at  the  electrodes. 
This  is  replenished  by  a  continual  stream  sent  out  from  the  bat- 
tery or  other  source,  and  the  net  effect  is  that  of  a  continuous 
current  of  electricity  flowing  thru  the  whole  system,  including 
the  solution.  The  electrical  conductivity  of  ionized  solutions 
has  given  them  the  name  of  "  electrolytes." 

The  source  of  supply  of  electrons  may  even  be  a  contact 


Copper  Wires 


Seat  of- 
Contact 
E.M.F. 


Beaker  with-*. 
Solution 


Fe 


Cu 
-   /- 


FIG.  48.— Electrolysis  by  Contact  E.  M.  F. 

electromotive  force.  In  Experiment  No.  6  it  was  shown  that 
the  joint  between  two  metals  of  unlike  chemical  composition 
or  physical  constitution  was  the  seat  of  a  "  contact  electro- 
motive force  "  projecting  positive  electrons  in  one  direction,  and 
negative  in  the  other.  The  potency  of  this  force  in  causing 
metallic  corrosion  by  methods  precisely  similar  to  those  studied 
may  be  demonstrated  by  apparatus  shown  in  Fig.  48. 

The  contact  between  the  iron  and  copper  is  a  seat  of  elec- 
tromotive force  discharging  positive  electrons  to  the  iron,  and 
negative  to  the  copper.  Dipped  into  a  dissociated  solution  (as 
of  sulfuric  acid,  for  instance)  the  iron  is  the  anode,  attracting  the 
sulfate  radical,  which  on  contact  becomes  a  chemical  entity  and 
attacks  the  iron  taking  one  atom  into  solution  for  each  two  par- 


198  EXPERIMENTAL  GROUP  IV 

tides  of  electricity  neutralized.  On  the  hand  the  hydrogen 
"  plates  out  "  on  the  copper,  accumulating  in  gas  bubbles. 

It  will  be  noted  that  the  current  flowing  in  this  system 
rapidly  drops  away  from  its  initial  value,  and  the  cell  is  then 
said  to  be  "  polarized."  This  is  principally  due  to  the  fact 
that  the  hydrogen  film  collecting  on  the  copper  is  a  poor  con- 
ductor of  electricity  like  all  gases  and  its  presence  largely  increases 
the  resistance  of  the  circuit.  With  a  constant  contact  electro- 
motive force,  the  current  passing  will  necessarily  vary  with  the 
total  resistance. 

It  was  found  in  Experiment  6  that  a  mere  difference  hi  physi- 
cal constitution  existing  between  two  metals  was  sufficient  to 
induce  a  contact  potential  at  their  joint.  In  this  connection  one 
can  easily  demonstrate  a  flow  of  current  in  an  electrolyte,  with 
the  consequent  corrosion  of  one  of  the  electrodes,  induced  by  the 
contact  potential  existing  between  a  hardened  and  an  annealed 
wire  of  exactly  the  same  chemical  composition.  Indeed,  our 
study  of  the  microscopic  constitution  of  steels  has  demonstrated 
the  essential  non-homogeneity  even  of  pure  iron -carbon  alloys. 
Practically,  all  commercial  irons  have  additional  discontinuities 
of  structure  due  to  slag  or  scale  inclusions,  segregations  of  ele- 
ments, or  physically  strained  spots  or  portions.  Each  border 
area  of  such  a  discontinuity  will  be  the  seat  of  contact  electro- 
motive force,  causing  differences  of  potential  at  various  portions 
of  the  metallic  surface. 

One  can  easily  explain  the  replacement  of  metal  from  solution 
on  this  basis.  Suppose  a  rod  of  commercial  iron  to  be  immersed 
in  a  solution  of  copper  sulfate.  Consider  the  action  of  two 
infinitesimal  areas  of  different  potential  (Fig.  49). 

The  copper  ion  will  be  attracted  to  the  negatively  charged 
area,  come  into  electrical  contact  and  plate  out  as  a  metal. 
The  S04  ion  will  be  attracted  to  the  positively  charged  area, 
come  into  electrical  contact,  the  charges  neutralize,  and  the 
SO4  becomes  chemically  active,  immediately  attacking  the  iron 
forming  iron  sulfate,  which,  being  soluble,  enters  the  solution 
and  is  dissociated.  In  this  manner,  all  the  copper  in  the  solution 


CORROSION 


199 


will  eventually  be  replaced  by  metallic  iron.  This  method  is  in 
extensive  use  in  copper  mining  districts  to  recover  the  copper 
from  the  mine  waters,  and,  indeed,  to  recover  copper  leached 
from  low-grade  tailing  dumps  by  rain  water. 

In  case  the  iron  is  dipped  in  very  dilute  salt  or  acid  solutions 
(tap  water)  the  case  is  somewhat  different.  Suppose  the  solution 
to  be  a  weak  solution  of  sulfuric  acid,  H2SO4.  As  discussed 
above,  different  surface  potentials  would  cause  a  migration  of 
the  ions,  the  hydrogen  plating  out  as  a  gas  film,  and  a  corre- 
sponding quantity  of  iron  sulfate  being  formed.  The  action  is 


Iron  Rod 


-Cu' 


-so4- 


Beakcr  with 

KCu   SO* 

Solution 


FIG.  49. — Electrolytic  Corrosion. 

quickly  polarized,  however,  owing  to  the  non-conducting  gas 
film  offering  a  very  large  resistance  to  the  electrical  interchange. 
This  is  not  the  case  if  iron  replaces  copper,  as  the  copper  plate  is 
an  excellent  electrical  conductor,  and  is  porous  enough  to  allow 
the  penetration  of  iron  and  sulfate  ions. 

Iron  in  the  purest  water  will  be  taken  into  solution  slowly, 
owing  to  the  fact  that  even  chemically  pure  water  is  slightly 
dissociated  into  (H)+  and  (OH)~.  The  result  of  the  interchange 
is  ferrous  hydrate, — rust.  Polarization  in  this  case  is  very  quick 
and  the  action  is  exceedingly  slow. 

Polarization  is  possibly  somewhat  akin  to  the  so-called 
"  passive  state  "  of  metals,  which  is  merely  a  temporary  sup- 


200 


EXPERIMENTAL   GROUP  IV 


pression  of  their  expected  action  (chiefly  as  far  as  solution  pres- 
sure is  concerned)  caused  by  dipping  the  metal  piece  in  a  strong 
oxidizer,  such  as  chromic  acid,  chromates,  or  strong  fuming 
nitric  acid.  The  passive  state  of  metals  is  not  yet  explained, 
but  it  may  be  that  the  action  of  the  oxidizer  changes  Fe++ 
(assumed  to  be  active)  into  Fe+"  "  (assumed  to  be  passive). 
Much  work  on  the  prevention  of  corrosion  has  been  done  with 
the  hope  of  discovering  some  method  of  making  the  metal 
permanently  passive. 

The  mechanism  of  the  rusting  of  iron  in  ground  water  may 
now  be  illustrated  in  the  following  experiment.     Ground  water  is 


Fe 


Fe 


Kesistance 


-==-  C  Yolt 
- — _  Battery 


Beaker  with 
\%  Salt  Solution 


FIG.  50. — -Mechanism  of  Corrosion. 

a  complex  solution  of  mineral  salts  with  more  or  less  oxygen  and 
carbonic  acid  in  solution — in  general,  it  is  an  oxidizing  substance. 
In  the  experiment,  in  order  to  hasten  the  action,  two  bars  of 
iron  are  used  for  electrodes  to  represent  areas  of  different  poten- 
tial, the  contact  electro-motive  force  is  replaced  by  a  battery, 
and  the  ground  water  represented  by  a  i  per  cent  salt  solution. 

The  salt  in  solution  is  dissociated  into  a  sodium  cation  and  a 
chlorine  anion,  the  former  of  which  is  attracted  to  the  negatively 
charged  electrode,  and  the  chlorine  to  the  other.  On  coming 
into  electrical  contact  the  chlorine  becomes  a  chemical  atom, 
extremely  corrosive,  and  attacks  the  iron,  according  to  the  fol- 
lowing equation : 

Fe+Cl3  =  FeCl3. 


CORROSION  201 

The  iron  chloride  is  soluble,  enters'  into  solution  and  is  dis- 
sociated. 

The  sodium,  on  the  other  hand,  attacks  the  water  of  the 
electrolyte  as  follows: 


the  sodium  hydrate  is  soluble,  and  dissociates  in  solution,  while 
the  hydrogen  appears  on  the  electrode  in  gas  bubbles. 

Soon  the  OH  ion  meets  an  iron  ion  in  its  migration,  and  the 
reaction 

3NaOH+3FeCl3  =  Fe(OH)3+3NaCl 

proceeds;  the  insoluble  iron  hydrate  (rust)  being  formed  in 
large  quantities  with  the  constant  regeneration  of  the  salt  in  the 
electrolyte. 

It  can  be  appreciated  that  only  a  small  electromotive  force 
and  a  small  amount  of  salt  is  sufficient  to  do  irreparable  damage 
to  a  piece  of  metal  if  a  constant  supply  of  water  is  available, 
and  the  action  does  not  become  polarized. 

The  following  list  of  factors  affecting  corrosion  from  Cushman 
and  Gardner,  "  Corrosion  and  Preservation  of  Iron  and  Steel," 
page  123,  needs  no  further  discussion  if  the  preceding  experi- 
ments are  understood 

Factors  which  Stimulate  Corrosion,  i.  Impure  and  segre- 
gated metal.  Unhomogeneous  or  burnt  metal  which  may  con- 
tain blowholes. 

2.  Cold-rolled  or  improperly  annealed  metal  which  may  main- 
tain an  uneven,  stressed  or  strained  condition. 

3.  Contact  action,  in  which  different  types  of  iron  and  steel 
are  used  in  one  and  the  same  structure. 

4.  The  presence  of  hydrogen  ions  from  any  source  whatso- 
ever that  may  be  brought  in  contact  with  the  surface  in  water 
or  other  electrolytes  in  the  presence  of  oxygen. 

5.  The  concentration  of  active  oxygen  that  is  present  in  the 
wetting  medium. 

6.  The  presence  of  electrolytes  generally  in    the   wetting 
medium. 


202  EXPERIMENTAL  GROUP  IV 

7.  The  stimulating  or  depolarizing  effects  of  certain  coatings 
applied  to  iron  and  steel  with  the  object  of  protecting  the  metal. 

8.  The  effect   of  indentations,   scratches  or  other  injuries 
which  become  centers  of  corrosion. 

9.  The  effect  of  extraneous  or  stray  currents  escaped  from 
high-potential  circuits. 

Factors  which  Inhibit  Corrosion,  i.  In  most  cases,  the 
reverse  of  the  conditions  which  stimulate  corrosion. 

2.  Contact   with   certain   substances   in   solution,    such   as 
chromic  acid  and  its  soluble  salts,  which  produce  a  passive  con- 
dition. 

3.  Alkaline  solutions  of  all  kinds,  where  the  concentration 
of  hydroxyl  ions  is  sufficiently  high.     But  this  protection  may 
be  overcome  in  very  strong  boiling  solutions. 

4.  Contact  with  more  electro-positive  metals. 

Much  matter  regarding  corrosion  is  now  being  published, 
both  by  interested  corporations  and  disinterested  scientists.  The 
results  of  short-time  tests  seldom  form  a  basis  for  comparison 
on  account  of  the  extreme  complexity  of  the  reactions,  and  the 
difficulty  of  adequately  controlling  the  influencing  factors.  This 
can  be  seen  from  a  consideration  of  the  following  list  of  factors 
affecting  the  rate  of  corrosion,  prepared  and  discussed  by  Friend : 

1 .  Quantity  of  dissolved  oxygen  in  water. 

2.  Area  of  exposed  metal. 

3.  Superficial  area  of  water. 

4.  Depth  of  immersion. 

5.  Pressure  of  oxygen. 

6.  Rate  of  motion  of  water. 

7.  Partial  immersion. 

8.  Physical  condition  of  iron. 

9.  Light. 

10.  Temperature. 

11.  Presence  of  rust. 

12.  Time. 

13.  Biological  influences. 


CORROSION  203 

One  very  beautiful  experiment  called  the  "  ferroxyl "  test 
has  been  developed  by  Walker  to  show  the  actual  migration  of 
iron  ions  away  from  the  solid  bar.  The  reagent  ferroxyl  is  a 
gelatine  which  contains  two  delicate  indicators;  phenolphthalein 
and  potassium  ferricyanide,  the  former  of  which  will  turn  pink 
in  the  presence  of  the  basic  ion  (OH)~  and  the  latter  turns  blue 
in  the  presence  of  iron  (Fe)++. 

If  then,  a  piece  of  iron  is  immersed  in  the  gelatine,  the  pres- 
ence of  a  pink  area  will  indicate  a  negative  node,  while  the 
presence  of  a  blue  zone  will  indicate  a  positive  node:  iron  is 
being  corroded  at  this  point.  The  gelatine  is  present  merely  to 
offer  greater  resistance  to  the  migration  of  the  ions,  i.e.,  to  "  fix  " 
the  reaction. 

Such  substances  as  litmus,  phenolphthalein,  methyl  orange, 
and  potassium  ferricyanide  are  called  "  indicators  "  because  they 
show  the  presence  of  slight  traces  of  certain  reagents.  Phenol- 
phthalein, for  instance,  is  a  very  weak  acid,  a  compound  of 
phenol  (carbolic  acid)  and  naphthalic  acid  (another  coal-tar 
derivative);  it  is  not  dissociated  in  a  neutral  solution,  and  is, 
therefore,  colorless.  However,  if  a  soluble  base  is  added,  a 
thalic  salt  is  formed  with  the  positive  ion  from  the  base,  which 
thalic  salt  does  dissociate,  when  the  characteristic  rose-colored 
Lhalic  ion  immediately  colors  the  solution.  Phenolphthalein 
is  thus  an  indicator  of  hydroxyl  ions,  i.e.,  of  bases,  to  a  dilution 
of  i  part  in  3  million. 

Homogeneous  steel — free  from  segregation  and  physical 
strains — undoubtedly  is  a  better  rust-resistant  material  than  an 
impure,  poorly  made  article.  There  is  reason  to  believe,  how- 
ever, that  the  best  wrought  iron  is  a  superior  material;  perhaps 
because  of  the  mechanical  protection  afforded  by  the  inert  slag 
inclusions.  Busy  iron  (such  as  rails  and  pipe  carrying  running 
water),  usually  last  better  than  otherwise,  perhaps  because 
the  mechanical  forces  break  up  and  spread  the  nodes  so  that 
localized  pitting  is  impossible.  It  is  also  known  that  spongy 
rust  is  electro-negative  to  iron  and,  therefore,  accelerates  cor- 
rosion; knowing  this,  the  engineer  should  insist  upon  thoro 


204  EXPERIMENTAL   GROUP  IV 

cleaning  before  painting  or  repainting  a  metallic  structure. 
Mill  scale  (FesCU),  on  the  other  hand,  is  electro-positive  to  iron, 
and  is,  therefore,,  an  inhibitor;  could  iron  be  so  treated  that  the 
rusting  would  form  the  magnetic  oxide,  the  corrosion  problem 
would  be  solved,  as  far  as  ferrous  materials  are  concerned.  The 
corrosion  in  boilers  or  hot  water  systems  is  ordinarily  combated 
by  hanging  slabs  of  zinc  in  the  boiler.  The  trouble  with  this 
practice  is:  First,  the  difficulty  of  getting  a  good,  durable, 
electrical  contact  between  the  metals;  second,  the  protection 
offered  by  the  zinc  is  localized;  and,  third,  it  is  uneconomic 
to  burn  zinc  to  save  iron.  A  better  way  to  control  such  cor- 
rosion is  to  eliminate  the  oxygen  from  the  feed-  and  circulating- 
water  (which  is  the  biggest  culprit  in  this  case)  by  boiling  it  in 
an  open-top  container  before  injecting  it  into  the  system. 

Special  Apparatus.     The  special   apparatus  required  is  as 
follows : 

Direct-current  ammeter,  lo-ohm  resistance. 

Millivoltmeter. 

Four  250-cc.  beakers. 

Two  test-tubes,  with  perforated  corks. 

f-in.  round  metal  rods  as  follows: 

One  of  copper. 

Five  of  mild  steel, 

Two  of  zinc. 
1 2 -in.  piece  of  steel  wire. 
Hand  towel, 
o.i-gram  trip  balance  and  weights. 

Supplies.     The  supplies  required  are  as  follows: 

N 


Sugar  solution, 


10 


N 
Sulfuric  acid  solution,  —  and  25  per  cent. 

Copper  sulfate  solution,  i  per  cent. 
Potassium  bichromate,  10  per  cent. 


CORROSION  205 

N 
Sodium  chloride  solutions,  —  and  2  per  cent. 

Freshly  prepared  warm  ferroxyl,  liquid. 
Spool  of  magnet  wire. 
Solvent  alcohol. 
Distilled  water. 
Metallic  fragments. 
i6-gage  steel  plate,  iX2-in. 
•     i6-gage  ingot  iron,  iX2-in. 

Laboratory  Equipment.  The  laboratory  equipment  required 
is  as  follows : 

6-volt  battery  circuit. 
Soldering  outfit. 
Quenching  bath. 
Buffing  wheel. 
Ice. 

Procedure,  a.  Arrange  the  apparatus  as  shown  in  Fig.  47, 
page  196,  to  test  the  conductivity  of  a  i  per  cent  sugar  solution. 
Does  any  current  flow,  as  indicated  by  the  ammeter?  Replace 
the  ammeter  by  a  millivoltmeter,  and  test  again  for  the  passage 
of  any  current. 

b.  Rearrange  the  apparatus  as  at  first,  and  test  the  conduc- 
tivity of  a  i  per  cent  sulfuric  acid  solution.     Verify  the  state- 
ments of  the  general  explanation,  page  196,  for  this  case. 

c.  Arrange  the  apparatus  as  shown  in  Fig.  48,  page  197,  to 
show  the  current  generated  by  the  primary  cell  "  copper  vs. 
iron,"  verifying  the  statements  of  the  general  explanation. 

d.  Cut  a  i2-in.  piece  of  steel  wire  in  two  pieces,  anneal  one 
piece,  and  harden  the  other.     Clean  these  wires,  connect  them  to 
the  ammeter  and  dip  the  free  ends  into  the  sulfuric  acid  solu- 
tion.    Observe  conditions  for  several  minutes. 

e.  Polish  a  mild  steel  rod  on  a  buffing  wheel,  wash  in  alcohol 
and  distilled  water.     Fill  a  test-tube  with  distilled  water,  and 
immerse  the  rod  by  holding  in  place  with  a  perforated  cork. 
Set  aside  and  leave  it  undisturbed,  examining  it  from  time  to  time, 


206  EXPERIMENTAL   GROUP   IV 

/.  Clean  another  steel  rod  as  in  procedure  e  and  dip  the  end 
of  it  in  a  i  per  cent  copper  sulfate  solution  for  five  seconds. 
Remove  and  wipe  off  quickly.  Repeat  the  operation,  dipping 
deeper  and  deeper  with  subsequent  immersions  until  a  visible 
copper  plate  is  formed  on  the  end,  which  cannot  be  wiped 
off. 

g.  Clean  another  rod  as  in  procedure  e,  and  immerse  for  an 
hour  in  a  10  per  cent  solution  of  potassium  bichromate.  Remove, 
wash  and  dry  on  a  clean  cloth.  Then  repeat  procedure/  until  a 
deposit  of  similar  density  is  acquired. 

h.  Assemble  the  apparatus  as  shown  in  Fig.  50,  page  200,  to 
show  the  electrolytic  theory  of  corrosion  of  iron. 

i.  Run  a  little  ferroxyl  into  the  bottom  of  two  beakers,  and 
place  in  ice  water  to  solidify.  Cool  the  balance  of  the  reagent 
nearly  to  the  solidification  point.  Clean  several  iron  fragments, 
such  as  a  needle,  a  bent  case  nail,  a  thin  black  sheet,  etc.,  as  in 
procedure  e,  place  them  on  the  ferroxyl  bed,  and  cover  with  the 
reagent.  Cool  the  whole  until  it  gels,  and  set  away  to  be  exam- 
ined on  the  morrow. 

j.  Clean  small  pieces  of  tinned,  galvanized,  and  terne  plates; 
dip  them  into  just-fluid  ferroxyl  to  give  a  thin  film  on  the  sur- 
face of  the  metal.  Set  away  to  be  examined  on  the  morrow. 

k.  Fill  two  beakers  with  a  2  per  cent  solution  of  NaCl.  In 
one  Of  them  place  an  iron  and  a  zinc  electrode,  not  in  electrical 
connection;  and  in  the  other  similar  electrodes,  connected  by  a 
conductor.  Allow  the  cells  to  stand  overnight,  and  examine. 

/.  Clean  and  weigh  two  pieces  of  i6-gage  metal,  iX2-in., 
one  of  mild  steel,  and  the  other  of  pure  ingot  iron.  Immerse 
these  in  25  per  cent  sulfuric  acid  for  one  hour,  wash,  dry,  and 
re-weigh. 

Queries,  a.  Discuss  any  variation  noted  from  the  expected 
results  of  procedure  b,  c,  and  h. 

b.  What  does  procedure  a  indicate  as  to  the  ionization  of 
sugar  in  solution? 

c.  Present  the  experimental  data  of  procedure  d  and  explain 
the  reason  for  a  steady  decrease  in  current. 


CORROSION  207 

d.  What  does  procedure  e  disclose  as  to  the  solution  pressure 
of  iron  in  pure  water? 

e.  Discuss  the  results  of  procedure  /  and  g. 

f.  Sketch  and  explain  the  results  of  the  ferroxyl  tests.     Give 
the  chemistry  of  the  ferricyanide  indication  for  ferrous  iron. 

g.  Discuss  fully  the  results  of  procedure  k,  explaining  the 
chemical  reactions  in  both  cases,  and  the  composition  of  the  end- 
products. 

//.  What  would  happen  if  a  piece  of  lead  were  immersed  in  a 
copper  sulfate  solution?  Why? 

i.  Explain  why  a  "  gravity  cell  "  is  not  polarized  and  how 
it  maintains  a  nearly  constant  electromotive  force. 

j.  What  influence  should  purity  of  the  iron  have  upon  cor- 
rosion? Why  should  cast  iron  be  such  a  good  rust-resisting 
material  as  to  be  used  in  water  pipes? 


EXPERIMENTAL   GROUP  V 
FOREWORD  TO  THE   STUDENT 

The  two  following  experiments  are  an  introduction  into  the 
metallurgy  of  cast  iron.  Evidently  they  could  be  extended 
considerably  in  case  a  student  wished  to  specialize  in  this 
particular  branch  of  metallurgy.  Many  problems  could  be 
investigated  bearing  upon  the  composition  of  molding  sand, 
its  proper  preparation  and  manipulation,  and  the  application 
and  operation  of  the  various  styles  of  molding  machines. 
Much  of  these  and  other  problems  of  the  iron  founder  are  best 
studied  in  the  foundry  itself,  however,  as  molding,  core  making 
and  melting  troubles  are  there  intensified. 


EXPERIMENT  NO.  25 
MOLDING 

Object.  The  object  of  this  experiment  is  to  make  sand  molds 
for  a  simple  casting,  or  test  bar. 

General  Explanation.  The  general  subject  of  molding  is 
treated  at  length  in  Appendix  B,  page  269,  which  is  a  coordina- 
tion paper  written  by  Prof.  Max  B.  Robinson,  when  Instructor 
in  Coordination  in  the  Cooperative  Engineering  Course  of  the 
University  of  Cincinnati.  The  subject  needs  no  further  elabora- 
tion in  this  place,  as  the  student  will  study  Appendix  B,  as  well 
as  pages  304  to  314  of  Mills,  "  Materials  of  Construction,"  for 
a  general  view  of  the  subject. 

In  this  experiment,  instructions  will  be  given  for  making 
molds  for  test  bars,  after  the  methods  developed  by  W.  J.  Keep, 
and  now  in  very  extensive  use  thruout  the  United  States. 

Special  Apparatus.    The  special  apparatus  used  is  as  follows: 

Set  of  molder's  tools: 

Square-pointed  shovel. 

Sprinkling  can. 

Bench  rammer. 

Strike. 

Fine  riddle. 

Bellows. 

Slick  and  spoon. 

Four  iron  follow  boards,  with  brass  pattern  and  chills, 
gate  sticks,  and  pouring  basins,  complete. 

Supplies.    The  supplies  needed  are  as  follows: 

Molding  sand,  preferably  "  stove-plate  "  sand. 
209 


210  EXPERIMENTAL   GROUP  V 

Laboratory  Equipment.     The  laboratory  equipment  needed 
is  as  follows: 

Holder's  bench. 

Four  snap  flasks  with  bottom  and  top  boards. 

Four  weights. 

Broom. 

Procedure,  a.  Ask  an  instructor  to  examine  the  sand,  which 
has  been  left  from  the  previous  day's  work  in  a  neat  pile  near  the 
molding  bench.  This  sand  will  be  somewhat  too  dry  for  use. 
Shovel  the  old  sand  into  a  new  pile,  sprinkling  the  old  pile  with 
water  from  time  to  time  as  instructed.  Re-shovel  (or  "  cut  ") 
the  sand  at  least  three  times  more  to  reduce  it  to  a  uniformly 
damp  condition.  Prepare  a  few  shovelsful  of  unused  sand  for 
"  facing  "  in  a  similar  manner. 

b.  Use  the  iron  follow  board  furnished  by  the  stock  clerk. 
Place  it  on  the  molding  bench,  cleats  extending  away  from  the 
molder.     The  brass  pattern  will  fit  in  place  and  is  made  to  cast 
from  the  under  side  two  test  bars,  J  in.  by  J  in.  by  12  in  long. 
The  pattern  also  forms  the  skim  gate  and  runners.     Place  the 
chill  yokes  in  their  proper  place  on  the  follow  board.     Place  tht 
"  drag,"  or  lower  half  of  the  flask,  upside  down  over  the  follow 
board,  pins  thru  cleats. 

c.  Sift  the  facing  sand  thru  a  fine  riddle  to  cover  the  whole 
pattern  some  2  in.  deep,  and  tuck  in  gently  with  the  hands. 
Shovel  the  drag  full  of  old  sand,  ramming  it  around  the  edge  of 
the  flask  with  the  chisel  edge  of  the  rammer,  butt  end  inclining 
toward  the  center.     Round  off  the  remainder  of  the  sand  with 
the  hands,  and  butt-ram  the  entire  surface  vigorously. 

d.  Scrape  off  the  excess  sand  to  a  level  with  the  edge  of  the 
flask  with  a  "  strike  "  or  straight  edge,  sprinkle  on  a  little  loose, 
dry  sand  with  the  hands  and  rub  the  bottom  board  to  a  firm 
bearing. 

e.  Grip  the  entire  assemblage  of  follow  board,  drag,  and  bot- 
tom board,  and  turn  it  upside  down  ("  roll  over  ").     Remove 
the  follow  board,  by  lifting  vertically,  blow  off  any  loose  sand  with 


MOLDING  211 

a  bellows.  Ask  an  instructor  to  inspect  the  condition  of  the 
surface  before  proceeding. 

/.  Sprinkle  a  little  fine,  dry,  "  parting  "  sand  evenly  over  the 
entire  surface,  place  the  cope,  or  upper  half  of  the  flask  on  the 
drag,  pin  thru  cleats,  and  place  a  gate  stick  in  the  proper 
position. 

g.  Repeat  procedures  c,  d,  and  e  in  the  cope.  Before  the  cope 
is  rolled  over,  remove  enough  sand  alongside  the  gate  stick  to 
allow  the  fire-clay  pouring  basin  to  be  properly  embedded,  with- 
draw the  gate  stick,  and  round  and  smooth  all  edges,  patting 
down  the  sand  with  the  fingers. 

/z.  The  cope  is  now  upside  down  on  the  bench  beside  the  drag. 
Bevel  the  gate  hole  at  the  parting.  Withdraw  the  pattern  by 
lifting  it  vertically,  without  rapping.  Sprues,  runners  and  skim 
gates  need  not  be  cut  as  the  pattern  is  constructed  to  form  them. 
The  chills,  of  course,  are  to  be  left  in  position,  embedded  in  the 
sand.  Be  particularly  careful  to  remove  the  last  bit  of  loose 
sand  in  the  mold.  Mark  the  mold  by  making  one  or  more  small 
conical  dents  in  the  sand,  so  that  the  finished  bars  will  have  dis- 
tinguishing marks  for  identification.  Finish  any  imperfections 
by  hand  or  "  slick,"  replace  the  cope  on  the  drag,  removing  the 
top  board.  Lift  the  bottom  board,  flask,  and  mold  to  the  floor 
where  it  can  be  poured,  and  place  a  flat  cast-iron  weight  on  the 
cope  to  hold  the  parting  tight  shut. 

i.  Each  squad-member  shall  make*  a  mold  individually,  calling 
upon  an  instructor  to  inspect  and  grade  his  work  at  the  end  of 
procedure  h.  At  the  end,  the  flasks  should  be  "  shook-out," 
that  is,  the  sand  returned  to  the  original  pile,  and  the  floor 
cleaned  up. 

Queries,     a.  Sketch  and  describe  a  molding  machine. 

b.  Sketch  and  describe  the  mechanical  arrangement  used  in 
"  vibrators  "  to  produce  the  rapid,  slight,  jarring  effect. 

c.  Why  is  it  necessary  to  peen-ram  with  a  tool  inclined  toward 
the  center  of  the  flask? 

d.  Describe  a  method  for  exact  control  of  the  moisture  in 
molding  sand. 


212  EXPERIMENTAL  GROUP  V 

e.  Discuss  the  limitations  of  molding.  For  instance,  why 
are  columns  usually  of  built  structural  shapes?  What  portion 
of  the  foundry  field  has  the  manufacture  of  "  stampings " 
appropriated?  What  methods  are  employed  to  cheapen  and 
expedite  "  quantity  production?" 

/.  Give  specifications  of  sand  for  molding  stove-plate;  gen- 
eral machine  parts;  brass;  steel. 


EXPERIMENT  NO.  26 
COMPOSITION  OF  CAST  IRON 

Object.  The  object  of  this  experiment  is  to  determine  the 
effect  of  chemical  composition  upon  the  physical  properties  of 
cast  iron. 

General  Explanation.  In  the  experiments  of  Group  IV,  the 
properties  of  steel  were  studied  with  the  aid  of  the  modern  equi- 
librium diagram,  Fig.  23,  page  131.  In  that  place  it  was  stated 
that  steels  may  be  regarded  as  iron-carbon  alloys  with  a  low 
percentage  of  carbon.  Similarly,  cast  iron  is  essentially  different 
only  in  having  a  higher  percentage  of  carbon  in  the  alloy.  The 
point  of  demarcation  may  be  taken  as  1.7  per  cent  carbon, 
98.3  per  cent  iron,  which  is  the  maximum  solubility  of  carbon 
in  iron,  that  is  to  say,  the  highest  carbon  austenite. 

Suppose,  now,  that  a  pure  alloy  containing  3  per  cent  carbon, 
97  per  cent  iron,  be  cooling  from  the  molten  state.  Reference  to 
Howe's  diagram,  Fig.  23,  page  131,  shows  that  at  1280°  C.  the 
first  particles  of  solid  appear.  This  solid  is  not  pure  iron,  how- 
ever, for  at  that  temperature  iron  and  carbon  form  a  solid  solu- 
tion having  a  carbon  content  of  0.6  per  cent.  Further  cooling 
would  dissipate  the  latent  heat  of  the  solidifying  austenite,  as 
well  as  the  sensible  heat  of  the  mixture,  and  the  temperature 
would  fall  gradually,  accompanied  by  a  continuous  solidifica- 
tion of  austenite. 

Examine  the  state  of  the  melt  at  1200°  C.  According  to  the 
equilibrium  diagram,  the  just-solidifying  liquid  must  have  a 
carbon  content  of  3.75  per  cent  carbon,  while  the  just-con- 
gealing solid  has  a  carbon  content  of  0.95  per  cent  C,  both  of 
composition  far  removed  from  those  at  1280°  C. — 3.0  per  cent  and 
0.6  per  cent,  'respectively.  The  first  crystal  of  austenite  formed 

213 


214  EXPERIMENTAL  GROUP  V 

at  1280°  C.  (containing  0.6  per  cent  C,  99.4  per  cent  Fe)  naturally 
enriched  the  remaining  mother  liquor  in  carbon  by  withdrawing 
a  high-iron  alloy  from  the  melt.  It  is  easy  to  see,  therefore, 
that  the  composition  of  the  mother  melt  must  slide  down  the 
liquidus  with  decreasing  temperature  until  the  eutectic  point 
(4.3  per  cent  C)  is  reached. 

The  variation-  in  the  carbon  content  of  the  progressively 
solidifying  austenite  is  not  usually  so  well  appreciated.  Just 
after  the  first  crystal  of  0.6  per  cent  austenite  has  formed,  it 
finds  itself  in  an  unstable  condition  at  a  slightly  lower  tempera- 
ture. The  0.6  per  cent  austenite  is  no  longer  the  saturated 
solution,  but  it  must  continuously  absorb  carbon  from  its  sur- 
roundings, becoming  higher  and  higher  in  carbon-content  to 
match  that  of  the  continually  solidifying  austenite.  In  this 
way  (if  time  be  given  during  a  slow  cooling),  the  already  solid 
austenite  is  absorbing  carbon  from  the  mother  liquor,  and  the 
whole  solid,  no  matter  at  what  time  its  parts  have  been  born,  has 
a  composition  which  slides  down  the  solidus  to  the  maximum 
solubility,  1.7  per  cent  C,  arriving  there  at  exactly  the  same 
time  and  temperature  as  does  the  mother  liquor  at  the  eutectic. 

At  this  instant,  the  mixture  contains  primary  crystals  approx- 
imating 1.7  per  cent  austenite,  and  eutectic  mother  liquor  of 
4.3  per  cent  carbon.  The  temperature  will  remain  constantly 
at  1130°  until  the  mother  liquor  has  solidified  into  an  euteclic 
mixture  of  1.7  per  cent  austenite  and  cementite,  cementing  the 
primary  crystals  together  into  one  solid  mass.  The  radiating 
heat  is  entirely  supplied  at  this  temperature  by  the  latent  heat 
of  solidification  of  these  two  components. 

A  further  cooling  of  the  entirely  solid  iron  will  bring  further 
changes.  As  the  temperature  falls,  the  saturation  solubility  of 
iron  carbide  in  iron  continually  decreases.  The  primary  massive 
crystals  of  austenite,  and  the  lamellar  eutectic  austenite  must 
both  progressively  eject  this  excess  of  cementite.  This  ejection 
is  continuous  until  a  temperature  of  720°  C.  is  reached,  when  the 
constitution  of  the  metal  is  made  up  of  0.9  per  cent,  austenite, 
cementite  bordering  this  austenite  (having  been  precipitated 


COMPOSITION   OF   CAST  IRON 


215 


therefrom)  and  lamellar  cementite  of  the  original  eutectic, 
which  might  be  called  'k  eutectic  cementite."  At  720°  C.  the 
remaining  0.9  per  cent  austenite  breaks  up  into  pearlite;  and  no 
further  change  should  take  place,  other  than  a  coagulation  of 
the  like  constituents  into  favored  areas. 

Such  is  the  constitution  of  the  purest  white  cast  iron,  and  it  is 
illustrated  in  Fig.  51  by  Wlist.  It  seems,  however,  that  if  more 
than  about  1.25  per  cent  of  carbon  is  present  in  the  alloy,  the 
cementite  acts  as  a  very  unstable  compound,  especially  at 


FIG.  51.— White  Cast  Iron.     (Wiist.) 

temperatures  lower  than  1100°  C.  On  even  moderately  slow 
cooling,  the  iron  carbide  breaks  up  into  ferrite  and  graphite, 
the  latter  accumulating  in  long,  greasy  flakes,  filling  in  a 
metallic  network  with  a  lubricant,  void  of  tenacity.  These 
flakes  give  gray  iron  its  characteristic  color  and  fracture,  and 
the  other  physical  properties  are  strictly  dependent  upon  the 
discontinuity  of  the  metallic  aggregate. 

Fig.  52,  by  Boylston,  shows  the  constitution  of  this  iron  to 
be  really  a  low-carbon  steel,  intersected  by  graphite  flakes. 

Intermediate  stages  in  the  decomposition  of  cementite  into 
graphite  and  ferrite  are  sometimes  encountered,  and  are  termed 


216 


EXPERIMENTAL   GROUP   V 


"  mottled  irons."     Fig.  53,  by  Wiist,  shows  their  constitution  so 
clearly  that  discussion  would  be  superfluous. 


FIG.  52. — Gray  Cast  Iron.     (Boylston.) 


FIG.  53.— Mottled  Iton.     (Wiist.) 

It  is  easy  to  see  that  the  physical  properties,  such  as  strength, 
shrinkage,  etc..  are  primarily  dependent  upon  the  amount  of 


COMPOSITION  OF   CAST  IRON  217 

carbon  present  and  its  state  of  aggregation.  For  instance,  dis- 
regarding the  total  carbon  present  in  cast  iron,  it  may  be  said 
that  carbon  as  cementite  ("  combined  carbon  ")  will  produce  the 
following  results: 

Combined  Carbon 

Softest  Iron  0.15  per  cent  or  less 

Iron  with  maximum  tensile  strength          0.45  per  cent 
Iron  with  maximum  transverse  strength   0.7  per  cent 
Iron  with  maximum  crushing  strength       i  .o  per  cent  or  more 

These  matters  have  been  thoroly  explained  by  Howe,  and 
the  student  is  referred  to  Mills,  "  Materials  of  Construction," 
pages  323  to  332,  for  their  discussion.  They  should  be  thoroly 
understood,  as  the  effect  of  other  alloying  metals  and  metalloids 
is  indirect,  chiefly  due  to  the  influence  they  exert  upon  the  state 
of  the  carbon. 

With  the  exception  of  sulfur,  it  is  impossible  to  detect  the 
presence  of  even  large  percentages  of  other  alloying  impurities 
in  cast  iron  by  microscopic  examination.  Silicon,  for  instance, 
is  thought  to  form  iron  silicides,  which  dissolve  in  the  ferrite  and 
somehow  produce  marked  instability  in  cementite. 

For  this  reason  it  may  be  said  that  silicon  should  be  kept 
within  the  following  limits  to  produce  the  indicated  results: 

Per  Cent  of  Silicon 

For  maximum  hardness  0.8  per  cent  or  less 

For  maximum  crushing  strength  0.8  per  cent 

For  maximum  density  and  modulus  of 

elasticity  i  .o  per  cent 

For  maximum  transverse  strength  i  .4  per  cent 

For  maximum  machinability  2.5  per  cent 

Sulfur  is  thought  to  form  an  iron  sulfide,  which  combines 
with  iron  to  form  a  low-melting,  tenuous,  weak  eutectic  which 
surrounds  the  crystalline  grains,  and  induces  great  red-shortness. 
It  also  counteracts  the  effect  of  fifteen  times  as  much  silicon, 


218  EXPERIMENTAL   GROUP  V 

and  consequently  should  be  kept  as  low  as  possible  (less  than 
0.15  per  cent)  in  good  gray  foundry  irons. 

Manganese  counteracts  the  action  of  sulfur  by  forming 
manganese  sulfide,  and  should  always  be  present  to  this  extent. 
The  manganese  sulfide  readily  liquates  and  may  burn  at  the 
surface  of  a  quiet  melt,  thus  eliminating  the  sulfur  from  tjie  iron. 
Excess  of  manganese  above  the  sulfur  requirement  forms  a 
double  carbide  with  iron,  and  thus  increases  the  combined  car- 
bon; more  than  i  per  cent  manganese  affects  the  mechanical 
properties  of  the  iron  directly  by  altering  the  characteristics  of 
the  pearlite. 

Phosphorus  probably  forms  a  solid  solution  with  ferrite, 
increasing  fluidity  and  producing  cold-shortness.  Its  effect  is 
much  masked  by  other  impurities,  however.  If  it  is  kept  below 
0.5  per  cent,  it  will  hardly  affect  the  strength  of  the  material; 
if  thin  castings  are  the  prime  consideration,  upwards  of  i  per 
cent  may  be  used. 

Numberless  analyses  of  irons  have  been  given  as  recom- 
mended practice  for  this  or  that  service.  Some  of  them  show 
such  small  variations  between  various  classes  of  castings  as  to 
be  well  within  the  limit  of  error  of  melting,  sampling  and  analysis. 
The  strength  and  adaptability  of  castings  depends  to  such  a 
great  extent  upon  molding,  melting,  pouring  and  annealing 
practice  that  it  is  dangerous,  if  not  foolish,  for  the  engineer  to 
specify  analyses  within  narrow  limits.  Even  if  the  foundryman 
luckily  furnishes  the  proper  analysis,  the  castings  could  easily 
be  of  inferior  grade  due  to  other  causes  than  the  conflicting 
influence  of  the  half-dozen  constituents  of  the  alloy.  For  infor- 
mation on  this  subject  the  student  should  first  read  T.  Turner's 
book  on  '*  Cast  Iron  "  and  his  article  in  the  Journal  of  the  Iron  and 
Steel  Institute,  volume  I  of  1886,  or  another  paper  on  the 
"  Analysis  of  Machinery  Irons,"  15  Metallurgical  and  Chemical 
Engineering,  683,  and  then  turn  to  the  Proceedings  of  the 
American  Foundrymen's  Association. 

Special  Apparatus.  The  special  apparatus  needed  is  as 
follows : 


COMPOSITION  OF  CAST  IRON  219 

Set  of  molder's  tools: 
Square-pointed  shovel. 
Sprinkling  can. 
Bench  rammer. 
Strike. 
Fine  riddle. 
Bellows. 

Slick  and  spoon. 
Three  iron  follow  boards,  with  brass  pattern,  chills  and 

gate  sticks  complete. 
o.i  m.g.  trip  balance  and  weights. 
Optical  pyrometer. 
Closed-end  observation  tube. 
Shrinkage  gage. 
Cold  cut. 
Graphite  electrode  for  stirring  rod. 

Supplies.     The  supplies  needed  are  as  follows: 

Three  fire-clay  pouring  basins. 

Molding  sand,  preferably  "  stove-plate  "  sand. 

White  cast  iron,  in  small  pieces  of  the  following  anal- 

ysis: 

C,  2.5  per  cent 
Si,  0.2  per  cent. 
P,  0.3  per  cent. 


, 
,1        as  low  as  possible. 


Gray  charcoal  iron,  in  small  pieces,  of  the  following  anal 

ysis: 


C,  3.5  per  cent. 

Si,  i.o  per  cent. 

P,  o.i  per  cent. 

S,  as  low  as  possible. 

Mn,  0.25  per  cent. 


220  EPXERIMENTAL  GROUP   V 

Powdered  and  analysed  alloys  as  follows: 

Pyrrhotite. 
Ferro-silicon. 
Ferro-manganese . 
Ferro-phosphorus. 

Laboratory  Equipment.  The  laboratory  equipment  needed  is 
as  follows: 

Molder's  bench. 

Three  snap  flasks,  with  bottom  and  top  boards. 

Three  weights. 

Broom. 

Platform  scales. 

Tilting  crucible  furnace,  with  annealed  crucible. 

Thermit  welder  crucible,  clay  lined. 

Cast-iron  pig-mold. 

Emery  wheel  with  wire  buffer. 

Impact  machine. 

Scleroscope. 

Anvil. 

Sledge. 

Procedure,  a.  Compute  the  amount  of  iron  necessary  to  pour 
three  molds  such  as  were  made  in  Experiment  No.  25.  Figure 
the  constituents  necessary  to  make  iron  of  the  composition  re- 
quired by  the  instructor,  weigh  and  charge  into  an  annealed 
graphite  crucible  in  a  tilting  crucible  furnace.  Start  the  gas 
flame,  gradually  increasing  the  temperature  to  a  maximum, 
with  a  reducing  flame. 

b.  Make  up  three  test-bar  molds  as  directed  in  experiment 
No.  25,  procedure  a  to  h,  inclusive.  Place  one  of  the  molds 
directly  underneath  the  opening  in  the  bottom  of  a  thermit 
welder  crucible,  and  the  whole  so  placed  that  the  furnace,  on 
tilting,  will  pour  a  stream  of  metal  which  will  strike  the  side  of 
the  welder  crucible,  and  from  this  be  delivered  to  the  pouring 


COMPOSITION  OF  CAST  IRON 


221 


basin   of  the  mold.     This  arrangement  is  shown  in  Fig.   54. 
Remove  the  flask. 

c.  When  the  iron  in  the  crucible  appears  to  be  thoroly 
molten,  observe  the  temperature  by  means  of  an  optical  pyrom- 
eter observing  a  closed  end  tube  thrust  thru  the  exhaust  hole 
into  the  crucible,  as  instructed  in  Experiment  15.  Obtain 
inspection  and  O.K.  by  the  instructor  before  proceeding. 


X^':V;M£'Flame  Exhaust 


Tilting  Crucible  Furnace 


Pyrometer 
'Observation  Tube 


Flame  Exhaust 


Hand  Wheel  and  Wo 
for  tilting  furnace 


Floor  Level 


FIG.  54. — Arrangement  for  Pouring  Test  Bars. 


d.  Without  shutting  off  the  gas  flame,  tip  the  furnace  over 
carefully,  filling  the  mold  with  a  thin  stream  of  metal.  Allow 
the  mold  to  cool  for  ten  minutes  and  carefully  shove  to  one  side, 
replacing  with  a  fresh  mold.  Pour  all  three  molds  in  this  manner 
with  iron  of  the  same  temperature.  Pour  any  excess  remaining 
in  the  crucible  into  an  iron  pig-mold.  In  pouring,  be  careful 
to  keep  a  steady  stream  running  continuously,  but  interrupt  it 
promptly  as  soon  as  the  pouring  gate  runs  full. 


222  EXPERIMENTAL   GROUP  V 

e.  Shake  out  the  castings  and  chills.  Saw  and  grind  off  the 
sprues,  and  brush  off  the  sand  with  wire  buffer.  Measure  the 
shrinkage  by  assembling  the  bar  and  its  corresponding  chill  on 
the  proper  follow  board,  and  slip  the  wedge-shaped  shrinkage  gage 
between  the  end  of  the  bar  and  the  chill  until  it  comes  in  contact 
with  each,  under  no  pressure  other  than  its  own  weight.  Read 
the  mark  at  the  upper  surface  of  the  bar  for  the  measure  of 
shrinkage. 

/.  Break  the  bars  in  a  beam-testing  machine  in  the  Strength 
of  Materials  Laboratory,  according  to  directions.  Observe  the 
fracture  for  size  of  grain,  color  and  segregation. 

g.  Take  three  of  the  bars  which  show  close  results  in  the  above 
test,  and  test  in  the  impact  machine,  after  procedure  /,  Experi- 
ment No.  17. 

h.  Explore  the  hardness  of  these  three  bars  with  a  sclero- 
scope. 

i.  Observe  and  sketch  the  depth  of  chill  by  splitting  the  ends 
of  the  bar  on  the  anvil  with  a  cold-cut. 

j.  Metallurgical  students  should  polish,  etch,  and  examine  the 
metal  under  the  microscope,  after  Experiment  No.  22. 

k.  All  sprues,  gates,  bars  and  fragments  should  be  reserved. 

NOTE.  Each  squad  should  have  individual  instructions  as 
to  the  analysis  of  iron  to  be  tested.  In  this  way  the  final  results 
can  be  examined  by  all  students,  and  will  exhibit  how  the  prop- 
erties of  cast  iron  vary  with  the  composition.  A  suggested  pro- 
gram of  such  variations  is  as  follows: 

Squad  i.  Melt  the  white  cast  iron  and  test  without  addi- 
tions. 

Squad  2.     Melt  the  gray  cast  iron  and  test  without  additions. 

Squad  3.  Melt  the  gray  cast  iron,  and  stir  continuously  for 
an  hour  with  thin  iron  wire. 

Squad  4.  Add  1.5  per  cent  silicon  as  ferro-silicon  to  the 
metal  from  Squad  i.  These  additions  in  every  case  should  be 
made  within  ten  minutes  of  the  time  of  pouring.  Drill  a  hole  in 
the  end  of  a  graphite  electrode,  put  in  the  weighed  amount  of 


COMPOSITION  OF   CAST  IRON  223 

powdered  alloy,  and  hold  in  place  with  a  wad  of  paper.  Use 
this  electrode  as  a  stirring  rod;  the  paper  will  char,  and  the  alloy 
will  be  introduced  below  the  surface  of  the  molten  metal  in  this 
manner. 

Squad  5.  Add  1.5  per  cent  silicon  as  ferro-silicon  to  the 
metal  of  Squad  2. 

Squad  6.  Add  enough  sulfur  as  pyrrhotite  to  counteract 
the  silicon  in  the  metal  of  Squad  4. 

Squad  7.  Add  0.75  per  cent  sulfur  as  pyrrhotite  to  the 
gray  cast  iron. 

Squad  8.  Add  i  per  cent  phosphorus  as  ferro-phosphorus 
to  the  white  cast  iron. 

Squad  9.  Add  i  per  cent  phosphorus  to  the  gray  cast 
iron. 

Squad  10.  Add  i  per  cent  manganese  to  the  white  cast 
iron. 

Squad  n.  Add  i  per  cent  manganese  to  the  gray  cast 
iron. 

Squad  12.  Add  i  per  cent  manganese  to  the  metal  from 
Squad  6. 

Queries,  a.  Make  up  a  neat  tabulation  of  the  properties 
of  the  cast  iron  investigated,  and  post  it  on  the  proper  bulletin 
board. 

b.  Make  a  tabulation  of  the  results  of  all  squads,  interpreting 
and  discussing  the  data  fully. 

c.  How  could  the  irons  be  tested  for  fluidity? 

d.  How  can  a  white  iron  be  changed  into  a  gray  iron  by  a  heat 
treatment? 

e.  Automobile  cylinders  are  to  be  made  of  the  following  com- 
position: 

Si : 1.75  per  cent 

S 0.08  per  cent 

P 0.40  to  0.50  per  cent 

Mn 0.60  to  0.80  per  cent 

The  foundryman  has  the  three  following  irons  available: 


224  EXPERIMENTAL   GROUP  V 

Iron  I  Iron  II  Iron  III 

Si 2.5  1 . 10  1 . 24 

S 0.04  0.07  O-O5 

P o .  80  o .  40  o .  50 

Mn o .  60  o .  30  o .  50 

Calculate  the  number  of  pounds  of  each  he  must  use  in  order 
to  make  the  required  analysis,  allowing  0.02  per  cent  gain  in 
sulfur  from  the  coke  in  the  cupola,  and  0.20  per  cent  loss  in  silicon 
due  to  oxidation  during  melting. 


APPENDIX  A 


ELEMENTARY  METALLURGICAL  CALCULATIONS 

Besides  noting  in  a  shorthand  form  the  reactions  which  are 
taking  place,  the  chemical  equation  also  gives  three  sets  of  quan- 
titative data:  First,  quantities  of  weights  involved;  second,  in 
the  case  of  gases,  quantities  of  volumes  involved,  and  third, 
quantities  of  heat  involved.  These  relations  will  be  briefly 
discussed  seriatim. 

The  Weight  Relation.  The  weight  relation  .follows  from  the 
rule  that  in  a  balanced  chemical  equation,  the  mass  of  the  dif- 
ferent materials  reacting  is  proportional  to  their  molecular 
weights.  The  symbolism 


is  a  shorthand  form  of  writing  the  fact  that  when  two  hydrogen 
molecules,  each  of  two  atoms,  combine  with  one  oxygen  molecule 
containing  •  two  atoms,  the  reaction  produces  two  molecules  of 
water,  each  containing  two  atoms  of  hydrogen  and  one  of  oxygen; 
furthermore,  the  combination  is  attended  with  the  liberation  of  a 
considerable  amount  of  heat,  whose  quantity  is  represented  by 
the  abstract  figure  116,120. 

The  weight  of  an  atom  of  hydrogen  is  taken  as  unity;  the 
weight  of  an  oxygen  atom  has  been  determined  to  be  1  6  times 
as  great.  We  therefore  compute  that  four  parts  of  hydrogen 
by  weight  burned  in  32  parts  of  oxygen  by  weight,  will  give  36 
parts  of  steam,  by  weight.  The  unit  of  mass  is  immaterial;  it 
may  be  the  weight  of  an  hydrogen  atom,  or  an  ounce,  pound, 
gram,  ton,  or  any  other  convenient  quantity.  The  point  to 
remember  is  that  whatever  the  weight  of  the  material  reacting, 

225 


226 


APPENDIX  A 


and  whatever  the  units  used  to  express  this  quantity,  these 
masses  will  be  proportional  to  the  abstract  numbers  representing 
the  weight  of  the  substances  appearing  in  the  balanced  equa- 
tion, i.e.,  the  "  reacting  "  weights,  computed  on  a  scale  in  which 
the  weight  of  the  hydrogen  atom  is  unity.  The  reacting  weights 
are  usually  noted  in  arable  numerals  below  the  symbol  of  the 
molecule,  the  above  chemical  equation  completed  to  show  the 
weight  relation  being 


4  +32=36. 

Atomic  Weights.     The  following  list  of  approximate  atomic 
weights  will,  therefore,  be  useful: 


Element. 


Symbol. 


Atomic  Weight. 


Hydrogen H 

Boron B 

Carbon C 

Nitrogen N 

Oxygen O 

Fluorine F 

Sodium Na 

Magnesium Mg 

Aluminum Al 

Silicon Si 

Phosphorus P 

Sulfur S 

Chlorine Cl 

Potassium K 

Calcium Ca 

Chromium Cr 

Manganese Mn 

Iron Fe 

Copper Cu 

Zinc Zn 

Tin Sn 

Antimony Sb 

Barium.  . Ba 

Mercury Hg 

Lead...  Pb 


i 
ii 

12 
14 

16 

iQ 

23 

24-3 

27.1 

28.3 

3i 

32.1 

35-S 

39-1 

40.1 

52 

54-9 

55-8 

63.6 

65-4 
118.7 

I2O.  2 

137-4 
2OO.6 

207.2 


ELEMENTARY  METALLURGICAL   CALCULATIONS      227 

In  addition  to  the  terms  atomic  weight  and  reacting  weight, 
the  chemist  uses  the  term  "  molecular  "  weight.  This  denotes 
the  abstract  number  formed  by  adding  together  the  atomic 
weights  of  the  atoms  constituting  the  molecule.  In  this  manner 
the  molecular  weight  of  sulfuric  acid  (H2SO4),  is  found  to  be 
98.1  as  follows: 

H2  =  2  atoms  at    i     =   2 

S  =  i  atom  at  32.1   =32.1 
64  =  4  atoms  at  16   =64 


H2SO4  =  i  molecule  at        98.1 

The  number  98.1  merely  means  that  the  molecule  of  sulfuric 
acid  weighs  98.1  times  as  much  as  one  atom  of  hydrogen.  In 
other  words,  the  weight  of  the  molecule  of  sulfuric  acid  is  98.1 
if  the  weight  of  an  atom  of  hydrogen  is  taken  as  unity.  This 
abstract  number  representing  the  molecular  weight  is  used  quite 
often,  and  the  abbreviation  "  mol  "  has  been  proposed  for  it. 
The  unit  of  weight  is  usually  prefixed,  as  follows:  one  gram- 
mol  of  sulfuric  acid  is  98.1  grams  of  the  pure  material.  Similarly, 
one  oz.-mol  of  water  would  weigh  18  oz. ;  three  kg.-mols  of  water, 
54kg.;  etc. 

Illustrative  Problem.  In  working  problems,  numerical  or 
otherwise,  the  student  should  cultivate  the  habit  of  preceding 
carefully  step  by  step,  rather  than  trying  to  arrive  at  the  con- 
clusion in  one  grand  leap. 

Step  i.  Read  the  problem  carefully  and  understandingly. 
"  What  weight  of  SCb  can  be  formed  by  the  combustion  of 
100  kg.  of  pyrite,  FeS2?  "  Apparently  the  compound  splits 
up,  and  the  sulfur  at  least,  burns  in  a  supply  of  oxygen  to 
form  sulfurous  acid  anhydride.  Disregarding  whatever  may 
happen  to  the  iron,  which  is  evidently  the  intent  of  the  query, 
proceed  to 

Step  2.     Symbolize  the  chemical  reaction 

The  compound  splits  up:  FeS2— »  Fe+S2±heat,~ 
The  sulfur  burns :  S2 +O2  ->  S02  ±  heat. 


228  APPENDIX  A 

This  is  merely  an  abbreviated  qualitative  statement  of  what 
happens.     This  should  next  be  adjusted  so  that  the  quantities 
balance,  and  the  two  reactions  added  together. 
Step  3.     Balance  the  equations 

Fe+S2±heat, 


Check  the  work  by  adding  the  number  of  atoms  on  both  sides  of 
the  equality  signs.  Add  the  equations,  cancelling  out  terms 
alike  on  both  sides: 


Step  4.     Check  the  equation  by  atoms 


i  FeS2  mol  with  i  atom  Fe  on  the  left;   i  atom  Fe  on  the  right. 

1  FeS2  mol  with  2  atoms  S  on  the  left;  2  mols  SO2  each  with  i 

atom  S  on  right. 

2  02  mols,  total  4  atoms  on  left;  2  mols  SO2  each  with  2  atoms 

O  on  right. 

The  equation  of  the  chemical  reaction  is  evidently  correctly 
written.  Proceed  to 

Step  5.  Re-read  the  problem,  and  decide  upon  the  next 
procedure.  "  What  weight  of  SO2  can  be  formed  by  the  com- 
bustion of  i  CXD  kg.  of  FeS2?"  Evidently  weight  is  required. 
Weights  vary  as  the  molecular  or  reacting  weights.  The  amount 
of  heat  evolved  or  absorbed  seems  not  to  be  required  in  the 
solution  of  the  problem,  and  it  will,  therefore,  be  disregarded 
hereafter. 

Step  6.     Compute  the  reacting  weights 

One  FeS2  has      i  Fe  atom  at  55.8     =55.8 
2  S  atoms  at  32.1     =64.2 


i  FeS2  molecule  at      120.0 


ELEMENTARY  METALLURGICAL   CALCULATIONS      229 
One  62  mol  has  2  O  atoms  at  16        =32.0 


2  62  molecules  at         32.0=   64.0 

One  S02  has        i  S  atom  at  32.1      =32.1 
2  O  atoms  at  16       =32.0 


2  SO2  molecules  at     64.1  =  128.2. 

The  complete  equation  is  now  written  with  the  weights  under- 
neath the  respective  reagents. 

FeS2+2O2  =  Fe  +  2SO2 
120.0+64.0  =  55.8  +  128.2. 

Check  by  addition     184.0     =     184.0     O.K. 

Step    7.  Interpret  the    results — be  very  careful  here.     The 
problem  (read  it)  asks: 

100  weights  FeS2  produce  x  weights  SO2? 
The  equation  says: 

1 20  weights  FeS?  produce  128.2  weights  SO2. 

These  two  statements  can  be  combined  and  worked  by  propor- 
tion; merely  draw  a  line  between  the  two  statements,  converting 
them  into  two  fractions: 

ICO  X 


120     128.2 

Whence  x  =  1^128.2  =  106.7  weight  units    of    SO2    (slide    rule 
computation).     The  weight  is  the  kilogram, 

Hence  106.7  kg.     Ans. 

Step  8.  Examine  the  result  as  to  whether  it  appears  rea- 
sonable. In  the  reaction,  one  Fe  weighing  55.8  is  replaced  by 
2Oi>  weighing  64.  The  resulting  gas  should  weigh  slightly  more 
than  the  original  pyrite.  106.7  kg.  is  slightly  greater  than  100 
kg.  The  answer  is  therefore  reasonable. 

This  procedure  may  seem  needlessly  profuse.     It  is  the  exact 


230  APPENDIX  A 

fashion  in  which  an  expert  would  subconsciously  solve  such  a 
problem,  and  it  is  insisted  that  all  problems  assigned  in  this 
course  be  attacked  by  the  beginner  in  the  same  manner.  The 
wording  of  the  thought  processes  need  not  be  written  out  at 
length,  but  all  problems  to  receive  credit  must  be  solved  in  an 
orderly  manner  following  the  above  example  condensed  into 
somewhat  the  following  style: 

Condensed  Solution. 

Problem.  —  Find  the  weight  of  metal  required  for  the  pro- 
duction of  gram-mol  of  its  oxide. 

Assumed  metal:  Al.     Assumed  oxide: 

Process: 


Balanced  equation 

Check  10  atoms  =  10  atoms     O.K. 

Reacting  weights    4A1  =  4  atoms  at  27.1  =  108.4 
362  =  6  atoms  at  1  6    =   96 

In  AhOs  are  A12  =  2  atoms  at  27.1=   54.2 
63  =  3  atoms  at  16    =  48 


2  mols  A^Os  at          102.2  =  204.4. 

Complete  equation :      4A1 +362  =  2A12O3  dzheat 

108.4+96  =204.4 
Check  204.4          =204.4    O.K. 

The  problem  asks  how  much  metal  to  give  gram-mol  of  oxide; 
i.e.,  xAl  to  give  102.2  gm.  AkOs. 

The  equation  says  108.4  Al  gives  204.4  A12O3. 
Divide  the  two: 

X       _I02.2t 
108.4       204.4' 

whence 

IO2.2       0 

x  = 108.4  =  54.2. 

204.4 


ELEMENTARY  METALLURGICAL   CALCULATIONS      231 

Answer:   54.2  grams  of  Al  will  form  gm.-mol  A12C>3. 

Is  the  answer  reasonable? 

The  problem  asks  how  much  Al2  in  A12O,3. 

2X27.1=54.2         O.K. 

Queries,  a.  Expand  the  above  condensed  statement  into 
the  form  of  the  illustrative  problem  given  just  preceding  it. 

b.  How  much  oxide  is  formed  from  1.7  Ib.  of  some  metal? 

c.  How  many  pounds  of  oxygen  are  required  to  burn  0.63  ton 
of  a  metal? 

NOTE.  —  Use  the  condensed  solution,  step  by  step,  for  queries 
b  and  c. 

The  Volume  Relation.  The  volume  relation  expressed  in  a 
chemical  reaction  involving  gaseous  materials  follows  from 
Avogadro's  law:  "  Equal  volumes  of  gas  under  like  temperature 
and  pressure  contain  the  same  number  of  molecules."  Another 
way  of  stating  this  law  is  that  the  volume  of  a  gas  is  proportional 
to  the  number  of  molecules  present,  or  more  simply,  that  all 
gaseous  molecules,  no  matter  what  their  composition  .  or  weight, 
occupy  the  same  space  (temperature  and  pressure  remaining  the 
same).  Be  careful  to  note  that  the  molecule  of  the  gaseous  ele- 
ments nearly  always  contains  more  than  one  atom,  usually  two. 
We  therefore  write 


rather  than 

H2+O  =  H2O  +  58,060, 

because  the  former  equation  states  a  reaction  between  two  stable 
gases  whose  molecular  formulae  are  H2  and  02,  respectively. 
The  latter  equation  states  a  reaction  involving  atomic  oxygen, 
which  is  incapable  of  continued  free  existence,  and,  therefore, 
represents  no  stable  substance. 

Furthermore,  since  the  former  equation  involves  molecular 
formulae  of  gases,  we  can  immediately  compute  that  two  volumes 
of  hydrogen  burning  in  one  volume  of  oxygen  will  produce  two 


232  APPENDIX  A 

volumes  of  steam.  This  volume  of  steam  produced  is  predicated 
on  the  condition  that  the  heat  generated  by  the  combustion 
(116,120  units)  has  radiated  into  cold  surroundings,  and  the 
product  of  the  reaction  has  cooled  down  to  the  temperature  and 
pressure  of  the  original  hydrogen  and  oxygen.  As  is  the  case 
with  weight  units,  these  volume  units  can  be  called  any  con- 
venient unit,  such  as  the  volume  of  a  gaseous  molecule,  or  a  cubic 
foot,  or  a  cubic  meter,  or  the  volume  of  a  gram-mol,  or  any- 
thing else.  The  unit  volumes  are  usually  expressed  in  Roman 
numerals  placed  above  the  symbol;  the  complete  chemical 
equation  showing  the  volume  relation  being: 

II       I         II 

=  2H2O+Il6,I20. 


Conservation  of  volume  is  not  existent,  as  is  conservation  of 
weight;  therefore  it  is  not  possible  to  check  this  step  by  adding 
the  volumes  on  either  side  of  the  equality  sign.  It  will  be  noticed 
however,  that  the  volume  unit  is  the  same  as  the  coefficient 
numeral  of  each  formula  representing  gaseous  molecules. 

Queries.  NOTE.  —  These  queries  are  to  be  worked  out  and 
recorded  step  by  step  after  the  method  of  the  condensed  solution, 
page  230. 

a.  How  many  cubic  feet  of  steam  at  100°  C.,  and  i  atmos- 
phere will  result  from  the  combustion  of  31.2   cu.ft.   ethane, 
C2H6,  measured  at  the  same  temperature  and  pressure? 

b.  How  many  cubic  meters  of  oxygen  are  required  to  burn 
7.35  cu.m.  of  ethane,  if  both  reagents  and  products  are  measured 
at  80°  F.  and  27  in.  of  mercury? 

c.  What  is  the  total  volume  of  all  the  products  of  combustion 
of  2.3  cu.in.  of  ethane,  if  all  gases  are  measured  at  the  same 
temperature  and  pressure? 

d.  If  air  is  a  mixture  of  gaseous  molecules  in  the  ratio  of  21 
molecules  of  Q2  to  79  molecules  of  N2,  how  much  air,  measured 
at  standard  conditions,  will  be  required  to  burn   1000  cu.ft. 
of  methane,  CHU,  measured  at  o°  C.  and  760  mm.  Hg. 

Heat  Evolution.     The  third  set  of  quantitative  data  given 


ELEMENTARY  METALLURGICAL   CALCULATIONS      233 

by  the  complete  chemical  equation  is  the  amount  of  heat  evolved 
or  absorbed  by  the  system  during  the  reaction.  The  reactions 
most  common  in  ordinary  experience  are  oxidations — the  burn- 
ing of  coal  or  gas  under  a  boiler  is  merely  a  progressive  chemical 
reaction  evolving  considerable  heat.  Other  reactions  common 
in  metallurgy  and  chemical  technology  absorb  heat  (are  "  endo- 
thermic  ")  and  would  quickly  stop  unless  that  amount  of  heat 
were  constantly  supplied  to  the  reagents  from  outside  sources. 

As  an  example  of  exothermic  reactions,  take  the  burning  of 
hydrogen  and  oxygen  in  the  oxy-hydrogen  blowpipe,  which 
produces  a  very  high  temperature — sufficient  to  fuse  silica  and 
platinum.  The  quantity  of  heat  evolved  by  this  reaction  has 
been  determined  by  experiment,  using  the  calorimeter  (see 
Chapter  7,  Franklin  and  Macnutt,  "General  Physics")-  It 
has  been  found  in  this  manner  that  four  kilograms  of  hydrogen 
burning  in  32  kg.  of  oxygen  and  producing  thereby  36  kg.  of 
steam,  will  produce  enough  heat  to  raise  the  temperature  of 
116,120  kg.  of  water  i°  C.,  if  the  heat  is  also  abstracted  from  the 
hot  products  of  combustion  by  cooling  them  down  to  the  original 
temperature  of  the  gaseous  reagents. 

The  quantity  of  heat,  116,120,  is  therefore  correct  for  the 
basis  of  "  from  and  at  zero  ";  that  is  to  say,  the  weighed  amount 
of  oxygen  and  hydrogen  were  at  o°  before  the  combustion,  and 
the  resulting  steam  has  been  cooled  to  that  same  temperature 
without  condensation.  The  116,120  heat  units  in  a  free  oxy- 
hydrogen  flame  are  mostly  absorbed  in  heating  the  resulting 
steam  to  high  temperature — in  a  calorimeter  the  sensible  heat 
of  the  hot  steam  is  abstracted  and  included  in  the  final  result. 

The  metric  unit  for  measuring  heat  is  called  the  "  calory," 
and,  in  quantity,  is  that  amount  of  heat  which  is  required  to 
raise  the  temperature  of  i  gin.  of  water  i°  C.  Inasmuch  as  the 
calory  is  a  rather  small  unit,  and,  furthermore,  as  there  are  many 
units  of  mass  in  common  use,  and  at  least  two  thermometric 
scales,  it  is  well  to  designate  the  heat  unit  by  terming  the  calory 
a  "  gram-degree-Centigrade,"  or  abbreviated  into  gm.-°C.  It 
will  be  found  very  convenient  to  use  larger  units  of  heat,  cor- 


234  APPENDIX  A 

responding  to  larger  units  of  mass,  such  as  the  kg.-°C.;  lb.-°C.; 
oz.-°C.;  oz.-°F.,  or  lb.-°F.,  which  last,  by  the  way.  is  the  British 
thermal  unit  (B.t.u.). 

In  the  above  calorimeter  experiment,  the  unit  of  weight — kg. 
—was  the  same  thruout;  therefore,  the  equation  is  correctly 
written  as 

2H2+O2      =  2H2O+u6,i2okg-°C. 
4  kg. +32  kg.  =  36  kg. 

As  long  as  the  Centigrade  thermometer  is  used,  the  number  of 
heat  units  (116,120),  will  be  correct  for  the  reacting  weights  of 
the  substances  involved.  The  kind  of  heat  unit  in  that  case, 
depends  only  upon  the  unit  of  mass  used  in  the  computation. 
Thus,  4  Ib.  of  hydrogen  burning  in  16  Ib.  of  oxygen  will  evolve 
116,120  lb.-°C.  units  of  heat;  32  grams  of  oxygen  burned  in 
hydrogen  will  evolve  116,120  gm.-°C.  units  of  heat.  Conversely, 
36  oz.  of  water  will  absorb  116,120  oz.-°C.  units  of  heat  on  becom- 
ing dissociated. 

The  figure  116,120  does  not  remain  true  if  the  Fahrenheit 
thermometer  is  used,  because  the  Fahrenheit  degree  represents 
only  |  that  absolute  difference  in  temperature  which  the  Cen- 
tigrade degree  denotes.  The  lb.-°F.,  for  instance,  which  is  that 
amount  of  heat  which  raises  one  pound  of  water  i°  F.,  is  only  f 
the  quantity  of  heat  as  that  represented  by  the  lb.-°C.,  the  latter 
being  that  amount  of  heat  which  raises  i  Ib.  of  water  i°  C.  It  is 
clear,  therefore,  that  while  the  combustion  of  4  Ib.  of  H2  will 
raise  116,120  Ib.  of  water  i°  C.,  the  same  quantity  of  heat  will 
raise  209,020  Ib.  of  water  i°  F. 

Thermochemical  Data.  Since  the  amount  of  heat  absorbed 
or  evolved  by  chemical  reactions  cannot  be  predicted  a  priori,  it 
is  necessary  to  furnish  a  list  of  calorimetric  results.  The  fol- 
lowing heats  of  formation  are  abstracted  from  a  more  complete 
list  in  Part  I,  of  Richards,  "  Metallurgical  Calculations,"  and  are 
arranged  in  each  class  according  to  the  atomic  weight  of  the  basic 
element.  All  heat  units  are  for  degrees  Centigrade,  and  on  the 
basis  "  from  and  at  zero." 


ELEMENTARY  METALLURGICAL  CALCULATIONS      235 


REACTION 

Aluminates: 

3Ca+  2  Al-f  3O2  =  (CaO)3(Al2O3)  +  789,050 

Berates: 

4Na+8B+7O2=  2Na2B4O7+  1,  496,200 

Carbides: 


Carbonates: 

2Mg+2C+302=  2MgCO3+539,8oo 
4Na+2C+3O2  =  2Na2CO3+S47,40o 
2Ca+2C+3O2  =  2CaCO3+547,7oo 
2Na+H2+2C+3O2=  2NaHCO3+  454,000 

Hydrates: 

2A1+3O2+3H2=  2Al(OH)3+6o2,6oo 
N2+5H2+02  =  2NH4OH+i77,6oo 
Ca+O2+H2  =Ca(OH)2+2i5,6oo 

Hydrocarbon  gases: 

C  +  2H2  =  CH4+22,25o  (methane) 
2C+3H2  =  C2H6+26,65o  (ethane) 
2C+2H2=C2H4-u,25o  (ethylene) 
6C+3H2  =  C6H6-  7,950  (benzene) 
2C+  H2  =  C2H2-  54,  750  (acetylene) 


Nitrides: 


Oxides: 


2NH,+24,4oo  (gas) 


2H2  +  O2 
2C  +  O2 
C  +  O2 

4Na+  O2 
2Mg+  O2 
2A12  +302 
Si  -f  O2 
4P  +sO2 
+  02 
+  €^ 


2H2O  +116,120  (gas) 
2CO    +  58,320  (gas) 
CO2     +  97,200  (gas) 
2Na2O+2oi,8oo 
2MgO+  286,800 


S 
4K 


2Fe 
4Fe 
3Fe 

4Cu+ 


SiO2  +196,000 
2P2O6  +730,600 
SO2  +  69,400  (gas) 
2X20  +196,400 
2CaO  +263,000 
2FeO  +131,400 
2Fe203+39i,2oo 
Fe3O4  +270,800 
2Cu2O+  87,600 


REACTING  WEIGHTS 

.2+96=270.5 

92X88+224  =  404 
40.1  +  24=    64.1 


48.6+24+96=168.6 
92      +24+96=212 
80.  2  +  24+96=200.  2 
46  +  2  +  24+96=168 


54.2+96+6=156.2 
28       +IO+32=     70 
40.I+32+    2=     74.1 


12+4=16 
24+6  =  50 

24+4=28 
72+6=78 
24+2  =  26 


28+6=54 


+    32  = 

+  32= 

+    32 


4 

24 
12 

92     -|-  32 

48.6+  32 

108.4+  96 

28.3+  32 

124     +160 

32.1+  32 

156.4+  32 

80.2+    32 
III. 6+    32 

223.2+  96 
167.4+  64 

254.4+    32 


36 
56 

44 
=  124 
=  80.6 
=  204.4 
=  60.3 
=  284 
=  64-1 
=  188.4 

=  112.2 
=  143-6 
=  319.2 
=  231.4 
=  286.4 


236 


APPENDIX  A 


Oxides: 
2Cu 
2Zn 
2Pb 
Pb 


REACTION 

O2  =  2CuO  +  75,400 
O2=2ZnO  +169,600 
O2  =  2PbO  +101,600 
O2  =  PbO2  +  63,400 


Silicates: 

4Na+  2Si+302  =  2  (Na2O)  (SiO2)  +  65  2  ,  200 
2Ca+2Si+3O2  =  2(CaO)(SiO2)+6s8,7oo 
6,Ca+2Si+5O2=2(CaO)3(SiO2)  +  i!2o6,io 


2Zn 

Sulfates: 

H2+S+202  = 
Ca+S+2O2  = 
Fe+S+2O2= 
Cu+S+2O2  = 
Zn+S+2O2  = 
Pb+S+2O2  = 


=  2  (ZnO)(SiO2)+  549,600 


:H2SO4+I92,2OO 

=  CaSO4+3i7,40o 
=  FeSO4+ 2 14,500 
=  CuSO4+i8i,7oo 
=ZnSO4+ 2  29,600 
=  PbSO4+2i5,7oo 


Sulfides: 

H2+S  =  H2S+  4,800  (gas) 
Fe+S  =  FeS+ 24,000 
2Cu+S  =  Cu2S+ 20,300 
Cu+S  =  CuS+ 10,100 
Zn+S  =  ZnS+43,ooo 
Pb+S  =  PbS+ 20,200 


REACTING  WEIGHTS 

127.2+  32  =  159.2 

130.8+  32  =  162.8 

414.4+  32=446.4 

207.2+  32  =  239.2 


92  +56.6+96=244.6 
80.2  +  56.6+  96=232.8 
240.6  +  56.6+160  =  457.2 
III.6  +  56.6+  96  =  264.2 
130.8  +  56.6+  96=283.4 


2  +32.1+64=  98.1 
40.1+32.1+64=136.2 
55.8  +  32.1+64=151.9 

63 . 6+32 . 1+64=  159 . 7 

65.4+32.1+64=161.5 

207.2+32.1+64  =  303.3 


=  34-1 
=  87.9 

=  159-3 

=  95-7 
=  97-5 
=  239-3 


55-8+32. 
127.2  +  32. 

63.6+32. 

65.4+32. 
207.2+32. 


Thermal  Calculation.  As  an  example,  take  this  problem: 
"  Required  the  number  of  pounds  of  carbon  to  be  burned  to 
raise  the  temperature  of  100  Ib.  of  water  from  40°  F.  to  200°  F." 

Step  i .  How  many  heat  units  are  required  to  heat  the  water? 
Assume  the  heat  unit  most  nearly  fitting  the  conditions  of  the 
problem,  i.e.,  lb.-°F. 

Temperature  at  end 200°  F. 

Temperature  at  beginning 40 


Increase 160°  F. 

Weight  of  water  heated 100  Ib. 

Heat  units  required  =  100  Ib.  X 160°  F.  =  16,000  lb.-°F. 


ELEMENTARY  METALLURGICAL  CALCULATIONS      237 

Step  2.     How   much    heat   will    burning    carbon    produce? 
From  the  complete  equation,  taken  from  the  above  lists, 


(gas) 
1  2  +  3  2  =  44  Check  this. 

This  equation  means  that  12  Ib.  of  carbon  burning  to  CO2  will 
give  off  97,200  lb.-°C.  units  of  heat. 

The  combustion  of  i  Ib.  of  carbon  will  evidently  produce 

^^  or  8100  lb.-°C.  units  of  heat. 

12 

Step  3.     Read  the  problem  and  appraise  the  results  so  far 
obtained. 


One  pound  of  carbon  gives   8,100  Ib.-  C.  heat  units. 
How  much  carbon  will  give  16,000  lb.-°F.  heat  units? 


Step  4.  The  units  of  heat  are  not  alike,  and  must  be  made  so. 

i  lb.-°C  =  *lb.-°F. 
The  combustion  of  i  Ib.  of  carbon,  therefore,  gives 

1x8100  =  14,580  lb.-°F.  heat  units. 
Step  5.     Solve  by  proportion. 

One  pound  burning  carbon  gives  14,580  lb.-°F. 
How  much  carbon  to  give  16,000  lb.-°F.? 

i     14,580 


x     16,000' 
16,000 


i.io  Ib.  carbon  required. 


14,580 

Answer. 
Step  6.     Is  the  answer  reasonable? 

12  Ib.  C.  will  boil  972  Ib.  water  from  o°  C. 

i  Ib.  C.  will  boil  approx.  80  Ib.  water. 

The  problem  calls  for  bringing  100  Ib.  water  nearly  to  a  boil. 
The  answer  should,  therefore,  be  nearly  i  Ib.  O.K. 


238  APPENDIX  A 

•  This  result  gives  the  minimum  amount  of  carbon  theoretically 
required,  on  the  basis  that  the  product  of  combustion  (CO2),  is 
cooled  to  o°  C.  Practically,  considerably  more  would  be  needed 
to  furnish  the  heat  carried  away  by  the  carbon  dioxide  escaping 
at  a  somewhat  higher  temperature — at  least  as  great  as  200°  F., 
the  temperature  of  the  absorbent  in  this  problem. 

Queries.  NOTE. — These  are  to  be  solved  and  recorded  step 
by  step. 

a.  How  many  gm.-°C.  of  heat  will  be  evolved  in  changing 
10  gm.  Fe  into  each  of  its  oxides? 

b.  How  many  lb.-°F.  will  be  evolved  in  burning  12  Ib.  CO 
to  CO2? 

c.  The  reaction 

2H2+02  =  2H20  +  ii6,i2o  (gas) 

is  on  the  basis  that  the  resulting  steam  is  cooled  to  o°  C.  and 
remains  gaseous  at  that  temperature.  What  will  be  the  heat 
evolution  of  the  reaction  on  the  basis  that  the  resulting  steam  is 
cooled  to  o°  C.  and  condenses  into  water,  if  the  condensation  of 
i  kg.  steam  at  o°  C.  into  water  at  o°  C.  evolves  606.5  kg.-°C.  units 
of  latent  heat? 

d.  Figure  the  heat  evolution  of  the  same  equation,  product 
solid  at  o°  C.,  if  the  latent  heat  of  fusion  of  i  Ib.  of  ice  is  144  B.t.u. 

Decomposition  of  Compounds.  All  the  thermal  equivalent? 
listed  above  correspond  to  the  formation  of  the  compound  from 
its  elementary  constituents.  The  great  number  of  ordinary 
reactions  are  between  compounds,  rather  than  elements.  In 
order  to  find  the  net  heat  effect  of  such  reactions,  it  is  evidently 
necessary  to  compute  the  input  of  heat  necessary  to  decompose 
the  reagents  into  their  constituent  elements,  and  deduct  this 
amount  from  the  total  heat  evolved  upon  their  reassembly. 

For  example,  to  evaluate  the  balanced  reaction 

C0+Fe203  =  C02  +  2FeO±heat, 

first  compute  the  amount  of  heat  necessary  to  decompose  the 
reagents  into  their  components,  as  follows 


ELEMENTARY  METALLURGICAL  CALCULATIONS       239 

Step  i.     Transpose  from  the  tabulation  of  thermochemical 
data  the  reactions 


—  391,200. 

These  equations  state  that  it  requires  an  input  of  58,320  heat 
units  to  decompose  2  mols  of  CO,  and  391,200  heat  units  to 
decompose  2  mols  of  Fe2O3.  Evidently  to  decompose  i  mol  of 
CO  will  require  29,160  and  i  mol  of  Fe2Oa  will  require  195,600, 
or  a  total  of  224,760  heat  units  to  decompose  the  reagents  into 
their  components  C,  Fe,  and  O2. 

Step  2.  Now,  after  this  decomposition  has  been  effected, 
the  atoms  recombine  in  a  new  array,  stated  in  the  following 
equations  : 

=  CO2+97,2oo, 


evolving  a  total  of  228,600  heat  units.  (The  original  equation 
involves  the  production  of  one  mol  of  CO2  and  two  mols  of 
FeO,  so  the  heat  figures  in  the  above  may  be  added  directly 
as  they  stand). 

Step  j.  Subtract  the  input  from  the  output. 

Input  ...............................   224,760 

Evolution  ............................   228,600 


Balance  evolved  ..................       3,840 

The  complete  equation  should  then  read. 


The  sign  would  have  to  be  minus  in  case  the  input  were  greater 
than  the  output,  in  which  case,  the  significance  would  be  that 
the  equation  absorbs  heat,  or  is  endothermic. 

Queries,  a.  Write  the  complete  equation  for  the  combustion 
of  the  gaseous  hydrocarbons. 

b.  How  much  heat  will  be  evolved  by  the  combustion  of  one 
kg.  of  these  hydrocarbons? 


240  APPENDIX  A 

c.  How  much  heat  is  evolved  in  the  reaction  of  water  on 
calcium  carbide,  forming  acetylene? 

d.  How  much  heat  is  evolved  in  the  "  thermit  "  reaction: 

Fe2O3  +  2  Al  =  A12O3  +  2Fe±heat. 

Gases.  Unless  otherwise  expressly  stated,  gases  are  measured 
by  volume  at  standard  conditions  of  temperature  (the  freezing 
point  of  water;  o°  C.,  or32°F.)  and  pressure  (one  atmosphere: 
760  mm.  or  29.9  in.  of  mercury;  or  14.7  Ib.  per  sq.  in.).  Should 
the  volume  be  desired  under  any  other  circumstances,  the  laws 
of  Gay  Lussac  and  of  Boyle  are  applied;  viz.,  that  the  volume 
of  a  gas  varies  directly  with  the  absolute  temperature,  and 
inversely  with  the  absolute  pressure.  Remember  particularly 
that  the  absolute  temperatures  are  used  in  figuring  the  volume 
of  gases,  and  that  absolute  zero  is  —273°  C. 

For  instance,  required  the  volume  of  189.9  cu.  ft.  of  gas  at 
500°  C.,  and  29.5  in.  pressure. 

773     29.9 
Solution.     Volume  required  =  189.9  X X  —  —  =  545  cu.  ft. 

Note  that  the  above  solution  can  be  made  by  multiplying  the 
original  volume  by  two  fractions,  one  fraction  made  up  of  the 
initial  and  final  temperatures,  and  the  other  made  up  of  the 
initial  and  final  pressures.  Trouble  with  such  problems  need 
never  be  experienced  if  the  temperatures  are  carefully  reduced 
to  the  same  thermometric  scale  in  degrees  above  absolute  zero, 
and  then  are  arranged  in  a  fraction  in  such  a  manner  as  to 
increase  the  volume  in  case  the  final  temperature  of  the  gas  is 
higher  than  the  original.  Then  carefully  reduce  the  pressures 
to  the  same  notation  (inches  of  mercury,  pounds  per  square  inch, 
or  what  not)  and  arrange  the  initial  and  final  pressure  into  a 
"  pressure  fraction  "  so  as  to  decrease  the  result  in  case  the 
final  pressure  of  the  gas  is  greater  than  the  original.  Or  vice 
versa,  in  either  case. 

Queries,  a.  If  the  pressure  of  i  atmosphere  is  equal  to 
that  of  760  mm.  of  mercury,  or  to  14.7  Ib,  per  sq.  in.,  figure  the 


ELEMENTARY  METALLURGICAL   CALCULATIONS      241 

specific  gravity  of  mercury  from  these  relations.  Given  that 
water  weighs  1000  oz.  per  cu.ft. 

b.  What  column  of  mercury  will  balance  the  pressure  rep- 
resented by  i  in.  of  water? 

c.  Figure  absolute  zero  in  degrees  Fahrenheit,  if  absolute  zero 
equals  —273°  C. 

d.  At  a  certain  point  in  a  flue,  89.9  cu.  ft.  of  gas  at  500°  F. 
and  740  mm.,  are  passing  per  minute.     What  will  be  the  quan- 
tity at  the  base  of  the  stack  when  the  gas  has  cooled  200°  and 
the  pressure  increased  by  the  pressure  of  i  in.  of  water? 

e.  If  the  above  gases  weigh  0.63  oz.  per  cu.ft.  at  the  base  of 
the  stack,  what  would  they  weigh  at  standard  conditions? 

Volume-weight  Relations.     In  the  complete  equation 

II      I         II 

2H2+O2  =  2H20+ 1 16,120, 

4   +32  =  36. 

The  volume  and  weight  relations  are,  in  general,  independent. 
For  instance,  it  cannot  be  said  that  4  Ib.  of  hydrogen  unite  with 
i  cu.  ft.  of  oxygen  to  make  36  Ib.  of  water,  because  i  cu.  ft.  of 
oxygen  does  not  weigh  32  Ib. 

From  Avogadro's  law,  page  231,  that  all  gaseous  molecules 
occupy  the  same  space  under  like  conditions  of  temperature  and 
pressure  no  matter  what  their  composition  and  weight,  it  should 
be  evident  that  a  quantity  of  one  gas  which  weighs  i  mol  should 
have  the  same  volume  as  another  which  also  weighs  i  mol. 
Thus,  i  gm.-mol  of  H2,  weighing  2  gm.;  i  gm.-mol  of  02,  weighing 
32  gm.;  i  gm.-mol  of  C02,  weighing  44  gm.;  etc.,  all  have  the 
same  volume,  for  this  good  and  sufficient  reason — that  they  all 
have  the  same  number  of  molecules.  The  volume  of  a  gm.-mol 
of  gas  has  been  called  a  gram-molecular-volume,  it  contains 
about  6.07  Xio23  molecules,  and  equals  22.4  liters  at  standard 
conditions.  Likewise,  a  kg.-mol-vol.  equals  22.4  cu.  m.,  and  an 
ounce-molecular-volume  equals  22.4  cu.  ft. 

This  idea  immediately  gives  a  method  of  computing  the 
specific  gravity  or  the  weight  per  unit  volume  of  any  gas  if  its 


242  APPENDIX  A 

molecular  composition  be  known,  or  of  any  mixture  of  gases  if 
the  percentage  composition  by  volume  is  determined. 

Illustrative  Problem.  "  Figure  the  weight  of  carbon  monox- 
ide (CO),  in  kilograms  per  cubic  meter,  at  standard  conditions." 

Step  i.  Kg.-mol-vol.  CO  occupies  22.4  cu.  m.  (By  rule 
above). 

C=I2 


kg.-mol  CO  weighs  28  kg. 

Step  2.     One  kg.-mol- vol.  weighs  i  kg.-mol. 

22.4  cu.  m.  weighs  28  kg. 
whence  i  cu.  m.  weighs  1.25  kg.  Answer. 

Queries,  a.  Compute  a  table  giving  the  formula,  molecular 
weight,  weight  per  cubic  meter  in  kilograms,  and  weight  per 
cubic  foot  in  ounces  of  each  of  the  following  gases: 

Hydrogen  Water  vapor 

Nitrogen  Carbon  monoxide 

Oxygen  Carbon  dioxide. 

b.  A  gram-mol-vol.  has  been  carefully  determined  to  be  22.39 
liters.  What  per  cent  of  error  is  involved  in  assuming  i  kg.-mol- 
vol.  to  be  22.4  cu.  m.?  What  per  cent  error  is  involved  in  assum- 
ing i  oz.-mol-vol.  to  be  22.4  cu.  ft.,  if  i  meter  =  39.3 7  in.  and  i  kg. 
equals  2.205  lb.* 


*  A  good  way  to  remember  the  mass  conversion  factor  is  as  follows:  There  are 
three  tons  in  general  use: 

i  short  ton  =  2000  Ib. 
i  long  ton    =224olb. 

X 

i  metric  ton  =  2 204  lb.  =  iooo  kg. 
whence  i  kg.  =2.204lb. 

Note  that  the  last  two  digits  are  merely  interchanged  in  the  case  of  long  and 
metric  tons. 


ELEMENTARY  METALLURGICAL  CALCULATIONS      243 

c.  Given  the  fact  that  air  is  a  mixture  of  approximately 
21  per  cent  oxygen  and  79  per  cent  nitrogen  by  volume,  what  is 
its  weight  per  cubic  foot  in  pounds?     In  ounces?    What  is  its 
weight  per  cubic  meter  in  kilograms? 

d.  From  the  above  data,  compute  the  percentage  composi- 
tion of  air  by  weight. 

e.  A  producer  gas  has  the  following  composition  by  volume: 

CO  24  per  cent 

C02  4 

H2  14 

CH4  3 

N2  55 

How  much  does  it  weigh  per  cubic  meter? 

/.  How  many  cubic  feet  would  90  Ib.  of  this  gas  occupy  if 
heated  to  235°  C.,  and  placed  under  2  atmospheres  pressure? 

Problems  in  Combustion.  The  relation  between  volume  and 
weight  is  very  important  as  it  is  the  starting  point  of  a  number 
of  calculations  necessary  for  designing  boilers,  furnaces,  flues  or 
stacks.  It  permits  the  computation  of  the  amount  of  air  nec- 
essary to  provide  for  the  combustion  of  any  fuel,  should  the 
analysis  of  the  latter  be  known.  It  also  enables  one  to  compute 
the  amount  and  analysis  of  the  flue  gases  produced  if  the  amount 
of  excess  air  is  known,  cr  vice  versa. 

Air  for  Combustion.  Given  an  anthracite  coal  of  the  follow- 
ing composition,  by  weight: 

C  90.0  per  cent 
H2          2.5 
02          2.5 
S  i.o 

H2O        1.0 
Ash         3.0 

required  the  cubic  feet  of  air  required  for  complete  combustion 
per  pound  of  coal,  under  forced  draft,  allowing  50  per  cent  excess 
air. 


244  APPENDIX  A 

Step  i.     The  reactions  involved  are 

a.  C+O2    =  CO2+97,2oo 
12+32     =44 

b.  2H2+O2    =  2H2O+n6,i2o 

4+32     =36 

c.  S+O2     =  SO2+69,26o 
32.1+32     =64.1 

Step  2.  Find  from  these  reactions  the  weight  of  oxygen 
needed  for  the  combustion  of  i  Ib.  of  coal,  by  the  methods  of  the 
illustrative  problem  on  page  227.  The  work  is  here  condensed 
to 

a.  O2  for  0.90  Ib.  C.;          C  :  O2  =  12     :  32  =0.90     :  x 

b.  O2  for  0.025  Ib.  H2;   2H2  :O2=  4     132=  0.025  :y 

c.  O2  for  o.oi  Ib.  S;  8:02  =  32.1:32=0.01    :  z. 

Solving  these  proportions :          x  =  2.400  Ib. 

3>  =  0.200  Ib. 
2  =  0.010  Ib. 


Net  oxygen  required  =2.6iolb. 

Step  3.     Some  oxygen  is  already  contained  in  the  coal,  and  a 
large  excess  is  provided. 

Net  O2  required 2 . 610  Ib. 

Less  O2  in  coal o . 025  Ib. 


Actual  requirement 2 . 585  Ib. 

Add  50  per  cent  excess i .  292  Ib. 


Total  O2  furnished . 3 . 877  Ib. 

Step  4.     The  problem  (read  it  carefully)  calls  for  cubic  feet. 

Oz.-mol-vol.  02  weighs  32  oz.  and  occupies  22.4  cu.  ft. 

Total  O2  given  weighs  3.877X16  oz.  and  occupies       x  cu.  ft. 


ELEMENTARY  METALLURGICAL   CALCULATIONS      245 

32  22.4 


By  proportion 


. 
3.877X16       x 


22.4X3-877X16  . 

Whence  x  =  —  -  =  43 .4  cu.  f t . 

Volume  of  oxygen  furnished  =  43. 4  cu.  ft.  per  Ib.  of  coal. 
Step  5.     The  problem  (read  it)  calls  for  cubic  feet  of  air. 

Air  is  21  per  cent  62  by  volume. 

43-4 
Total  air  furnished  = =  206.7  cu-  ft-  Answer. 

Step  6.     Is  the  answer  reasonable? 

Ewing,  "The  Steam  Engine"  page 449,  makes  the  statement 
that  about  12  Ib.  of  air  is  required  for  the  complete  combustion 
of  i  Ib.  of  coal.  Usually  12  Ib.  more  have  to  enter  the  fire-box 
if  it  is  operated  by  chimney  draft,  while  the  excess  can  be  cut 
down  by  50  per  cent  with  forced  draft. 

18X16 
18  Ib.  air  at  1.3  oz./cu.ft.= =22001.  ft.  approx. 

The  answer  is  reasonable. 

Composition  of  Flue  Gases.  The  percentage  composition 
of  the  flue  gases  or  their  volume  at  any  temperature  or  pressure 
may  also  be  calculated  in  the  following  very  condensed  solution 
for  the  anthracite  coal  just  above  (slide  rule  computation). 

COz  from  carbon  =3.300  Ib.,  equivalent  volume  =   26.9    cu.  ft. 

H^O  from  Hz  and  moisture  =  0.235  Ib:,  equivalent  volume  =     4.68 
SOa  from  sulfur  =0.02    Ib.,  equivalent  volume  =     o.n 

Oa  from  excess  air  =1.292  Ib.,  equivalent  volume=   14.45 

N2  from  total  air  =  163.3 


Total  products  at  standard  conditions  =  209.44  cu.  ft. 

The  percentage  composition  by  volume  is  now  easily  com- 
puted : 


246  APPENDIX  A 

CO2 12.8  per  cent 

H20 

S02 

02 

N2 

100.0  per  cent.    Check. 

Queries,  a.  Compute  the  volume  of  air  at  20°  C.  and  700 
mm.  necessary  to  burn  100  Ib.  of  the  producer  gas  mentioned  in 
the  query,  page  243,  allowing  25  per  cent  excess. 

b.  Compute  the  analysis  of  the  products  of  the  combustion  of 
this  producer  gas  by  volume. 

c.  A  long-flame  bituminous  coal  slack  containing  7.55  per 
cent  of  moisture   suitable  for  pulverizing,   is  first  dried   and 
crushed.     The  ultimate  analysis  then  shows: 

Sulfur 3.5  per  cent 

Hydrogen 5.1 

Carbon 74.2 

Nitrogen 1.2 

Oxygen 6.6 

Moisture 0.5 

Ash 8.9 

i oo.o  per  cent. 

The  coal  is  then  injected  into  a  cement  kiln  with  the  exact 
amount  of  air  for  combustion.  Compute  the  volume  of  air 
necessary. 

d.  Compute  the  analysis  of  the  products  of  the  combustion. 

e.  An  anthracite  coal  contains  by  analysis 

Carbon 89  per  cent 

Hydrogen .  3 

Oxygen i 

Ash......... 7 

100  per  cent. 


ELEMENTARY  METALLURGICAL  CALCULATIONS      247 

It  is  burned  under  a  boiler  producing  ashes  which  weigh  10 
per  cent  of  the  weight  of  the  coal  used.  (Assume  the  ashes  to 
contain  all  the  ash  of  the  coal  with  enough  unburned  carbon  to 
make  up  the  balance.)  The  dry  chimney  gases  analyze 

CO2 15.3  per  cent 

N2 80.4 

62 4.3  by  volume. 

How  much  excess  air  is  entering  the  fire-box? 

Total  Heat  of  Combustion.  It  should  be  evident  that  the 
total  heat  evolved  in  the  combustion  of  any  quantity  of  analyzed 
fuel  can  easily  be  determined  by  figuring  the  heat  resulting  from 
burning  its  constituents — carbon,  hydrogen,  sulfur,  or  any 
other  combustible  contained  in  unit  quantity  of  the  fuel — in  the 
manner  previously  outlined  on  page  236.  One  point  should  be 
carefully  noted,  however,  in  figuring  the  total  heat  of  combus- 
tion from  an  ultimate  analysis  of  a  solid  fuel  showing  oxygen. 
This  oxygen  appears  to  be  already  combined  with  carbon  and 
hydrogen  in  the  volatile  hydrocarbons  of  the  coal  in  such  a 
manner  that  it  may  be  assumed  (as  a  close  approximation  to  the 
actual  facts)  that  it  exists  as  water  (P^O).  For  this  reason,  all 
the  hydrogen  shown  in  the  analysis  is  not  available  for  heat 
production.  The  "  available "  hydrogen  is,  therefore,  that 
amount  shown  by  the  analysis  less  that  quantity  necessary  to 
satisfy  the  oxygen  also  present.  The  amount  of  carbon  available 
is  also  reduced  by  that  unconsumed  portion  entering  the  ashes. 

Illustrative  Problem.  Figure  the  heat  of  combustion  of  the 
anthracite  coal  mentioned  on  page  243,  if  the  dried  ashes  amount 
to  6  per  cent  of  the  original  coal. 

Step  i.     Copy  the  analysis  for  reference. 

C 90.0  per  cent 

H2 2.5 

02 2.5 

S i.o 

H2O i.o 

Ash 3.0  Check  it. 


248  APPENDIX  A 

Step  2.     Figure  the  available  hydrogen  and  carbon  ir.  i  Ib. 
of  the  coal. 

62  present  =  0.02 5  Ib. 
From  the  equation  2H2 + O2  =  2H2O  + 116,120 

4   +32=    36 

it  seems  that  the  oxygen  will  require  £  as  much  hydrogen  to  sat- 
isfy it,  weight  for  weight. 

Hydrogen  combined  =  |  0.025=0.003  Ib. 
Hydrogen  available  =  0.02 5  Ib.  present  minus  0.003  H>- 
combined  =  0.02 2  Ib. 

In  a  like  manner,  Ashes  produced  =0.06  Ib. 

Ash  from  analysis          =0.03  Ib. 


Carbon  in  ashes  =0.03  Ib. 

Carbon  in  analysis        =0.90  Ib. 


Available  carbon  =0.87  Ib. 

Step  3.  Figure  the  heat  resulting  from  the  combustion  of 
each  of  the  constituents.  Be  careful  to  use  the  available  quan- 
tities. 

a.  0.022  Ib.  H2  -»  H20  at  Il6>120  lb.-°C./lb.  =    639  lb.-°C. 

4 


6.0.87    Ib.  C   ->C02  at  -lb.-°C./lb.==  7,047  lb.-°C. 

c.  o.oi     Ib.  S    ->  S02  at    6gA°°  lb.-°C./lb.=      22  lb.-°C. 

32-1  _ 

Total  heat  from  i  Ib.  coal  =7,708  lb.-°C. 

Xl  gives  lb.-°F.      =  13,900  B.t.u. 

Answer. 

Step  4.     Is  it  reasonable? 
Anthracite  coal  is  nearly  pure  carbon. 


Pure  carbon  gives  =  8,100  lb.-°C./lb. 

Therefore  the  answer  is  reasonable. 


ELEMENTARY  METALLURGICAL  CALCULATIONS      249 

Queries,  a.  Compute  the  heat  of  combustion  of  the  pro- 
ducer gas  whose  analysis  appears  on  page  243,  in  B.t.u.  per 
100  cu.  ft.,  and  in  kg.-°C.  per  cubic  meter. 

b.  Natural  gas  from  the  West  Virginia  fields  has  the  following 
analysis : 

C2H4 0.4  per  cent 

CH4 93.0 

H2 2.0 

CO 0.6 

C02 0.3 

N2 3-0 

H2S 0.2 

Figure  its  heat  of  combustion  in  B.t.u.  per  1000  cu.  ft.,  and  in 
kg.-°C.  per  cubic  meter. 

c.  Gas  from  a  by-product  coke  oven  has  the  following  analysis: 

C2H4 2.4  per  cent 

CH4 29.2 

H2 50-5 

CO 6.3 

CO2 2.2 

O2 0.3 

N2 9.1 

Figure  its  heat  of  combustion  in  B.t.u.  per  1000  cu.  ft.,  and  in 
kg.-°C.  per  cubic  meter. 

d.  Compute  the  heat  of  combustion  of  the  bituminous  coal 
whose  analysis  appears  on  page  246. 

Proximate  Analysis.  The  production  of  an  ultimate  analysis 
of  any  fuel  is  a  slow  and  tedious  proceeding,  necessitating  the  use 
of  rather  special  and  expensive  apparatus.  Solid  fuels,  there- 
fore, are  usually  analyzed,  not  for  their  ultimate  constituents, 
carbon,  hydrogen,  etc.,  but  merely  for  moisture,  volatile  hydro- 
Carbons,  fixed  carbon,  and  ash.  (See  White,  "  Technical  Gas 
and  Fuel  Analysis,"  pages  193-208.)  These  latter  determina- 


250  APPENDIX  A 

tions  are  very  easily  made,  consisting  merely  of  weighing  the 
sample  before   and   after  certain  definite  heating  procedures. 
The  total  heat  of  combustion  can  be  figured  within  limits 
from  a  proximate  analysis  by  the  use  of  Goutal's  formula: 

Calorific  power  in  gm.-°C.  per  gram  =  82  C+kV. 

Where  C  is  the  percentage  of  fixed  carbon, 

V  is  the  percentage  of  volatile  hydrocarbons,  and 
k  is  a  factor  figured  by  interpolation  in  the  following 
table: 

V 

c+v  k 

°-°5 •-• 145 

0.12 124 

0.17 113       - 

O.26 IO2 

o-35  •  •  •  •  94 

0.40 80 

Illustrative  Example.     What  is  the  calorific  power  of  a  coal 
containing 

Volatile  hydrocarbons 10.05  Per  cent 

Fixed  carbon .86.7 

Moisture 1.8 

Ash 1.45 

Step  i.     Figure  a  value  for 


C+V 

Fixed  carbon 86.7  per  cent 

Volatile  hydrocarbons 10.05 


Total  fuel  matter.  .  .  .96.75 

Volatile  hydrocarbons     10.05 
Total  fuel  matter     =  96^75  =aio4- 


ELEMENTARY  METALLURGICAL   CALCULATIONS      251 

Step  2.     Figure  a  value  for  k  by  interpolation: 

0.05  =  145 

0.12  =124 


A  difference  of +0.07  makes  a  difference  of      —   21 


whence  +0.054  makes  a  difference  of     —   16.2  in  k 

V 

Then  when  =     0.05  and  k  =  145 

C-  ~t~  V 

and  the  corrections     =  +0.054  and  —   16.2 


V 
Then  if    —          =     0.104        £  =  128.8. 


Step  3.     Insert  these  values  in  Goutal's  formula. 

Calorific  power  =  82X86.7  +  128.8X10.05 
=  7109  +  1294 
=  8403  calories  per  gram  of  coal.     Answer. 

Step  4.  Is  it  reasonable?  Direct  calorimetric  experiments 
(see  Hofman,  "  General  Metallurgy,"  page  114)  gave  the  value 
8404  for  this  coal.  This  is  not  as  good  a  check  as  it  appears  to 
be,  inasmuch  as  the  bomb  calorimeter  condenses  all  the  water 
vapor  from  the  hydrogen  reaction  into  a  liquid.  This  bomb 
calorimeter  value  (which  is  easily  obtained  and  is  universally 
used  for  coal  valuation)  must,  therefore,  be  decreased  by  606.5 
calories  for  every  gram  of  moisture  formed  in  the  bomb,  in 
order  to  give  results  comparable  with  those  derived  by  com- 
putation from  analyses.  These  latter  are  on  the  basis  of 

2H2O+O2  =  2H20+  1  16,120  (gas). 

Goutal's  formula  may  be  of  prime  use  if  applied  to  coals  from 
a  certain  field,  whose  characteristics  are  known,  and  for  which  a 
new  list  of  values  for  k  may  be  derived  from  experience.  This 
formula  and  the  accompanying  values  of  the  constant  may  give 
quite  divergent  results,  however,  if  used  indiscriminately  for 
coals  from  different  regions. 


252  APPENDIX  A 

Queries,  a.  Figure  the  calorific  value  of  one  of  each  of  the 
several  types  of  American  coals  listed  on  page  177,  Hofman, 
"  General  Metallurgy,"  by  using  the  proximate  analysis,  and 
GoutaPs  formula.  Compute  the  percentage  error  in  each  case. 

High  Temperature  Reactions.  All  the  figures  given  for  the 
heat  evolution  of  the  various  reactions  listed  on  page  235, 
are  correct  only  in  case  the  reagents  are  originally  at  o°  C.,  and 
the  products  are  cooled  to  o°  C.  The  heat  abstracted  by  the 
cold  calorimeter  from  the  hot  products  of  the  reaction  is 
therefore  included  in  the  figures  representing  the  heat  effect; 
in  other  words,  the  reactions  proceed  "  from  and  at  zero." 

It  should,  therefore,  be  apparent  that  in  case  the  products  of 
any  reaction  (such  as  the  chimney  gases  from  a  boiler  setting) 
leave  the  focus  at  a  higher  temperature  than  o°  C.,  the  sensible 
heat  which  they  carry  away  with  them  must  be  deducted  from 
the  theoretical  maximum  thermal  equivalent.  Conversely,  any 
heat  brought  in  by  reagents  at  temperatures  above  o°  C.  should 
be  added  to  the  heat  evolved  by  the  reaction  as  such,  on  the  basis 
of  "  from  and  at  zero." 

We,  therefore,  construct  the  general  statement  that 

The  heat  evolved  by  any  reaction  equals  the  heat  of  the 
reaction  "  from  and  at  zero,"  plus  the  heat  in  the  reagents, 
minus  the  heat  carried  away  by  the  products. 

The  use  of  this  rule  presupposes  a  knowledge  of  the  amount 
of  heat  required  to  raise  the  temperature  of  various  bodies,  in 
other  words,  the  specific  heat. 

Specific  Heat.  The  amount  of  heat  required  to  raise  unit 
mass  of  a  body  thru  unit  temperature  is  called  the  specific 
heat  of  the  body.  Thus,  the  specific  heat  of  water  is  i  gm.-°C. 
per  gram — or  more  simply,  one  calory.  Water  requires  more 
heat  to  raise  its  temperature  than  any  of  the  common  substances, 
whose  specific  heats,  therefore,  are  expressed  by  fractional  ab- 
stract numbers.  For  instance,  the  following  short  table  taken 
from  Watson,  "  A  Text  Book  of  Physics,"  page  233,  gives 
the  specific  heat  of  some  common  substances  at  room  tem- 
peratures : 


ELEMENTARY  METALLURGICAL  CALCULATIONS      253 


Substance. 

At 

Specific  Heat. 

Ice  

-10° 

0.502 

Paraffin  wax                     

IO 

0.694 

Copper 

eo 

o  002 

Zinc  
Iron                                     

50 

1C 

0.093 
o.  109 

Platinum 

e,o 

o  032 

Mercury  
Petroleum                                            .... 

20 
4O 

0.0331 

o.  51 

The  specific  heat  is  not  a  constant,  but  its  value  usually 
increases  materially  with  higher  temperatures;  therefore,  in 
general,  it  takes  more  heat  to  raise  a  body  from  999°  C.  to  1000°  C. 
than  it  does  to  raise  the  same  substance  from  i°  C.  to  2°  C. 
This  statement  is  symbolized  by  the  equation 


where  H  is  the  heat  required  to  raise  the  temperature  of  a 
body  from  t  —  %°  to  2-fJ°;  a  is  the  specific  heat  at  o°  C.;  and  b 
is  a  numerical  coefficient.  For  the  purpose  of  elementary  met- 
allurgical calculations,  the  usual  problem  will  be  to  find  the  total 
heat  required  to  raise  a  body  from  o°  C.  to  t°  C.  The  numerical 
value  of  most  convenience  is,  consequently,  the  "  mean  specific 
heat,"  which  represents  the  average  value  of  the  specific  heat 
for  any  range  of  temperature.  Evidently,  the  mean  specific 
heat  is  a  function  of  the  temperature,  as  is  shown  in  the  following 
analysis: 

Specific  heat  at  o°  C.  =  a 

Specific  heat  at  t°  C.  =  a+bt 


Mean  specific  heat,  o°  to 


2a+bt 


a+-t. 

2 


This  is  the  average  amount  of  heat  required  to  heat  the  body 
i°  C.  The  total  amount  of  heat  required  to  heat  the  body 
t°  C.  is 

-°  to /°C.  =  («+-< 

2 


Total  heat,  o°  to  t°  C.  = 


254  APPENDIX  A 

that  is  to  say,  for  the  total  heat,  the  mean  specific  heat  must  be 
multiplied  by  /. 

The  following  tables  of  mean  specific  heats  of  gases  are 
abstracted  from  more  extensive  lists  in  Vol.  I,  Richards,  "  Metal- 
lurgical Calculations,"  and  the  values  are  true  either  for  calories 
per  liter,  kg.-°C.  per  cu.m.,  or  oz.-°C.  per  cu.ft. 

GAS  MEAN  SPECIFIC  HEAT 

Air 0.303+0.000027* 

Benzene,  CeHe o.  76 

Carbon  dioxide,  CO2 . 0.37  +o.  00022* 

Carbon  monoxide,  CO o. 303+0. 00002 7* 

Ethylene,  C2H4 .  o. 46  +o.  0003* 

Hydrogen,  H2 o. 303+0. 00002 7* 

Hydrogen  sulfide,  H2S o. 34  +o.  00015* 

Nitrogen,  N2 o. 303+0. 00002 7* 

Methane,  CH4 0.38  +0.00022* 

Oxygen,  O2 ' o . 303+0 . 000027* 

Sulfur  dioxide,  SO2 0.36  +0.0003* 

Water  vapor,  H2O 0.34  +0.00015* 

The  following  specific  heats  of  solids  are  for  calories  per  gram; 
kg.-°C.  per  kg.;  or  lb.-°C.  per  Ib. 

SUBSTANCE  MEAN  SPECIFIC  HEAT 

Alumina,  Al2Os o.  2081+0. 0000876* 

Antimony,  Sb 0.0486+0.0000084* 

Carbon,  C o.  2142+0.0001662 

Copper,  solid,  Cu o. 094  +o.  0000178* 

Copper  matte,  47  per  cent  Cu 0.211   —  o. 0000366* 

,   Copper  sulfide,  Cu2S o.  1126+0.00009* 

Hematite,  Fe2Os o.  1456+0. 000188* 

Iron,  Solid,  Fe o.  n     +0.000025* 

Iron  sulfide,  FeS o.  1357 

Lead,  solid,  Pb 0.0292+0. 000019* 

Lime,  CaO o.  1715+0.00007* 

Limestone,  CaCOs o.  2086 

Mercury,  Hg 0.0334—0.00000275* 

Silica,  SiO2 o.  1833+0.000077* 

Slag,  copper  blast  furnace o.  202  +0.0000302* 

Zinc,  solid,  Zn o. 0906+0. 000044* 

As  an  illustration  of  the  use  of  this  table,  the  total  sensible 
heat  above  o°C.,  in  i  cu.  ft.  of  air  at  4o°C.  is 

(0.303+0.000027X40)40  =  12.16  oz.-°C. 


ELEMENTARY  METALLURGICAL   CALCULATIONS      255 

The  second  factor  in  the  specific  heat  is  not  of  much  im- 
portance at  low  temperatures,  but  figure,  for  instance,  the  sensi- 
ble heat  in  i  Ib.  of  carbon  at  1000°  C.  It  is 

(o. 2 142  +0.000166 X 1000)  1000  =  380.2  lb.-°C. 

Net  Heat  of  Combustion.  The  practical  use  of  such  com- 
putations may  be  illustrated  as.  follows:  Suppose  the  anthracite 
coal  whose  composition  has  been  given  on  page  243,  is  burned 
under  a  boiler  producing  6  per  cent  ashes;  the  air  necessary 
for  complete  combustion  with  50  per  cent  excess  enters  the  fire- 
box at  40°  C.;  and  the  products  of  the  combustion  leave  the 
boiler  setting  at  200°  C.  How  much  heat  would  then  be 
available  for  steam  generation? 

Step  i.  Obtain  the  amount  of  heat  of  the  reactions  from  and 
at  zero.  Heat  of  combustion,  from  page  248  =  7708  lb.-°C.  per  Ib. 

Step  2.  Obtain  the  sensible  heat  brought  in  by  the  air  fur- 
nished for  combustion,  by  virtue  of  its  being  at  some  tempera- 
ture above  o°  C. 

The  amount  of  air  provided,  from  page  245,  =  206.7  cu.  ft  . 

Mean  specific  heat  of  air,  from  table  =  0.303+ 0.00002  7/ 

For  the  range,  o  to  40°  C.  =  (0.303+0.000027X40) 

Total  heat  in  i  cu.ft.  of  air,  from  o°  C.  to  40°  C. 

=  (0.303+0.000027X40)  X 40  oz.-°C.  =  12.16  oz.-°C. 
Total  heat  in  206.7  cu-  ft-  air  =  206. 7X12. 16  =  2510  oz.-°C. 
Reduce  to  same  unit  as  Step  i  =-fiP  =  157  lb.-°C. 
Step  3.     Obtain  the  sensible  heat  taken  out  by  the  smoke 
leaving  at  200°.     Condensing  the  detailed  operations  of  Step  2, 
and  obtaining  the  analysis  of  the  flue  gases  from  page  245. 

CO2..26.Q    cu.ft.x(o.37  +0.00022     X2oo)2oo=   2,225  oz.-°C. 
H2O.  .  .4.68  cu.ft. X (0.34  +0.00015     X2oo)2oo=      346 
SO2...  .0.11  cu.ft. X (0.36  +0.0003       X2oo)2oo=          9 

O2.  .  ..14.45  CU.ft.  X  (0.303 +O.OOOO27     X2OO)2OO=         891 

N2.  .  .163.3  cu.ft. X (0.303 +0.00002 7   X 200) 200  =  10,070 

Total  heat  in  gases =  13,541  oz.-°C. 

8461b.°C 


256  APPENDIX  A 

Step  4.  Apply  the  general  statement  of  high-temperature 
reactions.  The  net  heat  available  is  that  evolved  by  the  equa- 
tion from  and  at  zero,  plus  that  heat  brought  in  by  the  hot  air, 
minus  that  taken  away  by  the  flue  gases. 

Net  heat  =  7708 -f  1 57  —  846  =  7019  lb.-°C.  Answer. 

Regenerative  Principle.  The  advantage  of  using  heated  air 
in  a  furnace  is  easily  seen,  as  it  counterbalances  in  part  the  heat 
carried  up  the  chimney,  which  latter  can  amount  to  a  very  large 
amount  of  the  total  heat  generated  in  the  fire-box,  unless 
special  care  is  taken  to  keep  the  stack  temperature  low.  The 
temperature  of  the  gases  leaving  a  furnace  must  be  somewhat 
higher  than  the  temperature  required  for  the  operations  going 
on  within.  In  other  words,  a  steel  melting  furnace  must  be  at 
all  tunes  considerably  hotter  than  the  liquid  metal  (which  melts 
at  1530°  C.  or  less)  in  order  that  any  heat  may  flow  from  the 
heating  atmosphere  to  the  melting  slag  and  metal.  Flue 
gases  at  1600°  C.  or  more  carry  an  enormous  amount  of  sensi- 
ble heat,  and  this  would  be  entirely  wasted  if  passed  directly 
to  the  chimney.  Siemens'  regenerative  system  (see  Mills, 
"  Materials  of  Construction,"  pages  386-391)  utilizes  this  heat 
by  passing  the  hot  waste  gases  thru  a  brick  checkerwork, 
cooling  the  temperature  to  800°  C.  or  less.  This  heat  thus 
reclaimed  and  stored  in  the  hot  brickwork  is  returned  to  the 
furnace  by  reversing  the  gas  stream.  Cold  air  or  producer  gas 
now  go  in  the  opposite  direction,  arriving  at  the  furnace  ports  in 
highly  superheated  condition. 

Queries,  a.  The  producer  gas  whose  analysis  appears  on 
page  243  is  burned  in  20  per  cent  excess  air  in  an  open-hearth 
furnace.  The  gas  and  air  are  both  preheated  and  enter  the 
furnace  at  1000°  C.  The  products  of  combustion  leave  the 
furnace  at  1650°  C.  What  is  the  net  heat  effect  of  the  com- 
bustion? 

b.  Hot  air  at  800°  C.  from  the  stoves  is  blown  into  a  blast 
furnace,  meeting  incandescent  carbon  at  the  tuyeres  at  1580°  C. 
The  CO  formed  leaves  the  focus  at  1700°  C.  What  is  the  net 


ELEMENTARY  METALLURGICAL  CALCULATIONS      257 

output  of  the  reaction  in  heat  available  for  melting  iron  and 
slag? 

Maximum  Temperature  of  a  Flame,  or  Calorific  Intensity. 
The  problem  of  computing  the  maximum  temperature  attain- 
able by  a  reaction  is  solved  by  the  application  of  the  foregoing 
principles.  Evidently  the  highest  degree  (calorific  intensity), 
attainable  in  combustion  will  be  that  point  where  the  entire  heat 
evolution  of  the  equation  is  absorbed  by  the  products  of  the 
reaction.  In  other  words,  the  highest  temperature  attainable 
in  an  exactly  adjusted  oxy-hydrogen  blowpipe,  using  cold  gas, 
is  when  the  116,120  heat  units  evolved  in  the  combustion  is 
entirely  absorbed  and  carried  away  by  the  resulting  white-hot 
steam.  That  temperature  will  now  be  computed. 

Step  i.     The  reaction  is  2H2O+O2  =2H20+ 116,120  (gas) 

4+32  =36 

36  gm.  H20  will  absorb  116,120  gm.-°C.  of  heat. 

The  question  resolves  itself  into  this: 

If  36  gm.  steam  at  o°  C.  absorbs  116,120  gm.-°C.  of  heat, 
what  temperature  will  it  then  attain? 

Step  2.  The  specific  heat  of  gases  are  given  in  gm.-°C.  per 
liter. 

How  many  liters  of  steam  will  36  gm.  form,  at  standard  con- 
ditions? 

1  gm.-mol-vol.  steam  =  22.4  liters  =  18  gm. 

2  gm.-mol-vol.  steam  =  44.8  liters  =  36  gm. 

Step  3.  Form  an  equation  in  /  representing  the  total  heat 
in  this  steam,  from  o  to  some  unknown  temperature  /°C. : 

Mean  specific  heat  of  steam,  o  to  /°  =  0.34 +0.000152. 
Total  heat  of  steam,  o  to  f  =  (0.34 +0.0001  $t)t  per  liter 

=  44.8(o.34+o.oooi5/)/  for  36  gm. 

But  this  total  heat  is  to  be  equal  to  the  entire  product  of  the 
reaction,  i.e., 

44.8(0.34 +0.0001 5/)/  =  116,120. 


258  APPENDIX  A 

Step  4.     Solve  the  equation  for  t. 

Transposing,  o.oo6j2t2  +  i$.2$2t  =  116,120. 
This  is  a  quadratic  of  the  form  ax2+bx  =  c  whose  solution  is 

—  b±Vb2 -\-4ac 

$ . 

2d 

Substituting,  and  solving,  ^  =  3175°  C. 

Step  5.     Is  it  reasonable? 

This  temperature  seem?  very  high,  inasmuch  as  Burgess,  on 
page  456  of  "  Measurement  of  High  Temperatures,"  gives  the 
temperature  of  the  carbon  arc  as  3500°  €.±150°,  and  2200  to 
2300°  C.  for  the  temperature  of  the  oxy-hydrogen  flame  (page 
340).  The  solution  has  been  checked  over,  and  there  appear  to 
be  no  numerical  errors. 

The  trouble  may  be  in  the  value  for  the  specific  heat  of  water. 
This  physical  data  has  been  determined  for  moderate  tempera- 
ture, as  most  containers  become  permeable  to  gases  at  temper- 
ature near  or  above  1000°  C.  It  is  quite  possible,  therefore, 
that  the  formula  for  mean  specific  heat  should  have  a  third  term 
in  t2,  which  would  largely  increase  the  amount  of  heat  required 
to  heat  the  gas  at  temperatures  higher  than  1000°  C. 

Again,  it  may  be  possible  that  the  reaction  between  hydrogen 
and  oxygen  is  not  complete  at  such  high  temperatures  as  exist 
in  the  oxy-hydrogen  flame — in  other  words,  perhaps  only  about 
75  per  cent  of  the  gas  fed  to  the  flame  combines.  This,  of  course, 
would  cut  down  the  heat  evolved,  and,  consequently,  would 
largely  reduce  the  calorific  intensity. 

Queries,  a.  What  is  the  maximum  temperature  attainable 
in  burning  hydrogen  in  dry  air? 

b.  The  producer  gas  whose  analysis  appears  on  page  243,  is 
burned  in  20  per  cent  excess  air  in  an  open-hearth  furnace.     Both 
air  and  gas  enter  cold.    What  is  the  maximum  temperature 
attainable  in  the  furnace?    Would  it  melt  steel? 

c.  In  case  the  producer  gas  and  air  of  query  b  were  pre- 


ELEMENTARY  METALLURGICAL  CALCULATIONS      259 

heated  to  1000°  C.  by  regenerative  checkerwork,  what  would 
be  the  maximum  temperature  attainable  in  the  furnace? 

d.  Suppose  an  open-hearth  steel  plant  had  available  a  supply 
of  natural  gas  of  the  composition  shown  on  page  249.  This  gas 
cannot  be  preheated  because  the  hydrocarbons  would  decom- 
pose and  choke  up  the  checkerwork  with  carbon.  It  is,  there- 
fore, burned  cold,  and  only  the  air  preheated  to  1000°  C.  What 
would  be  the  maximum  temperature  attainable  in  this  case? 

Cementation  Index.  Portland  cement  has  been  denned  by 
A.  P.  Mills  (u  Materials  of  Construction,"  p.  92)  as  a  "  finely 
pulverized  product  resulting  from  the  calcination  to  incipient 
fusion  of  an  intimate  artificial  mixture  of  argillaceous  and  cal- 
careous materials."  The  relative  proportion  of  the  various 
constituents  lies  within  narrow  limits,  for  the  researches  of  S.  B. 
and  W.  B.  Newberry  show  the  essential  constituents  to  be  the 
tri-calcium  silicate  [(CaO)3(SK)2)L  and  the  di-calcium  aluminate 
[(CaO)2(Al203)]. 

In  the  compound  (CaO)sSi02,  the  ratio  of  base  to  acid  by 
weight  is  had  from  the  atomic  weights,  -as  follows: 

BASE  ACID 

Ca        =40.1  Si     =28.3 

O         =   16  O2    =  32 

CaO     =  56.1  SiO2  =  6o.3 

(CaO)3=i68.3 

Base  :  Acid  =  weight   (CaO)3  :  weight   SiO2  =  168.3  :  6°-3> 
whence 


Weight  CaO  =  ~  (weight  Si02)  =  2.8Xwt.  SiO2. 
00.3 

Similarly  in  the  compound  (CaO)2(Al203),  the  weight  ratio  is 
Base  :Acid  =  weight  (CaO)2  :  weight  Al20a  =  112.  2  :  102.2, 
whence 

112  2 

Weight  CaO  =  -  -  (weight  A1203)  =  i.i  X  wt.  A1203. 


260  APPENDIX  A 

The  relative  amounts  of  lime,  silica  and  alumina  required  to 
make  a  proper  mixture  for  cement  must,  therefore,  bear  the 
relation 

CaO  =  2.8SiO2+i.i  A1203, 

in  order  that  the  two  essential  constituents  may  have  sufficient 
material  for  their  formation.  The  formula  merely  states  that 
the  number  of  pounds  of  CaO  provided  in  the  "  slurry  "  entering 
the  cement  kiln  must  be  equal  to  2.8  times  the  number  of  pounds 
of  silica  plus  i.i  times  the  number  of  pounds  of  alumina. 

All  the  rocks  or  slags  available  for  the  manufacture  of  cement 
carry  a  considerable  amount  of  other  oxides.  Within  limits,  the 
most  important  of  these,  magnesium  oxide  (MgO),  is  commonly 
regarded  as  being  able  to  replace  the  basic  calcium  oxide  (CaO) , 
molecule  for  molecule,  while  the  iron  oxide  (Fe2O3)  molecule  acts 
as  an  acid,  and  is  the  equivalent  of  the  alumina  molecule  (A12O3). 
Other  compounds  in  the  raw  materials  are  purposely  kept  low, 
and  for  the  purposes  of  this  computation,  will  be  disregarded. 

On  the  basis  of  replacement,  molecule  for  molecule — or  more 
properly,  radical  for  radical — one  MgO  weighing  40.3  hydrogen 
atoms  will  replace  one  CaO  weighing  56.  i  hydrogen  atoms.  Or  in 
larger  units,  40.3  Ib.  MgO  will  replace  56.1  Ib.  CaO;  that  is  to 

say,  i  Ib.  MgO  will  replace Ib.,  or  1.4  Ib.  CaO.     Stated  in 

40.3 

other  words,  the  base  MgO  is  1.4  times  as  effective,  pound  for 
pound,  as  CaO,  and  the  magnesia  content  of  the  concrete  forming 
materials  will  replace  the  usual  base  (CaO)  in  that  proportion. 
The  formula  including  this  statement  then  becomes 

CaO+i-4  MgO  =  2.8  SiO2  +  i.i  A12O3. 

Following  a  similar  train  of  reasoning,  it  is  found  that  if  iron 
oxide  will  replace  aluminum  oxide,  molecule  for  molecule,  then 

Fe2O3  :  Al2O3  =  i59.6  :  102.2  =  1.1  10.7. 

The  .relation  which  must  finally  exist  is  expressed  by  the 
equation 

CaO+i.4  MgO  =  2.8  Si02-fi.i  Al2O3+o.7  Fe2O3. 


ELEMENTARY  METALLURGICAL   CALCULATIONS      261 

Transposing,  we  have  the  ordinary  statement  of  Eckel's  rule 
that 


2.8  SiO2  +  i.i  A12O3+Q.7  Fe2Q3_ 
CaO  +  i.4MgO 

If  a  cement  be  analyzed,  and  the  constituents  found  be  sub- 
stituted in  the  above  formula,  the  quotient,  or  "  cementation 
index,"  would  probably  not  equal  exactly  one.  A  cementation 
index  less  than  one  would  mean  that  an  excess  of  base  is  present  — 
that  free  or  uncombined  lime  may  possibly  be  present  in  the 
clinker.  In  order  to  be  sure  to  avoid  the  harmful  effects  pop- 
ularly attributed  to  "  free  lime,"  the  cement  chemist  ordinarily 
figures  his  mixture  for  a  cementation  index  approximating  i.i. 

Illustrative  Example.  As  an  illustration  of  the  use  of  Eckel's 
rule,  suppose  there  is  available  for  the  production  of  Portland 
cement  of  cementation  index  1.08,  the  following  materials: 

IRON  BLAST  FURNACE  SLAG  LIMESTONE 

CaO  =  49  .  8  per  cent  SiO2    =  3.9  per  cent 

SiO2  =33.2  A12O3  =   1.2 

A12O3  =  12.6  Fe2O3  =    i  .  o 

MgO  =  33  CaO  =53.5 

Fe2O3=   i.i  MgO  =0.8 

Assume  100  Ib.  slag  and  X  Ib.  limestone  as  a  basis  for  computa- 
tion.    Substituting  directly  in  the  formula 

2.8(33.  2  +0.039^0  +  1.  i  (i  2.  6+0.012^0  +0.7(1.  i  -j-o.oiX)  _ 
49.8+0.535^  +  1.4(3.3+0.008*) 

Multiplying,  as  indicated,  clearing  of  fractions  and  collecting,  we 
have 

0.46*=  48.8, 
whence 

X  =  io6\b. 

Consequently,  the  ingredients  should  be  combined  in  the  ratio 
of  loo  slag  to  1  06  limestone. 

Queries,     a.  Figure  the  analysis  of  the  above  cement.     Com- 


262  APPENDIX  A 

pare  this  analysis  with  the  average  figures  given  on  page  127  of 
Mills  "  Materials  of  Construction."  Discuss  the  probable  effect 
of  discrepancies. 

b.  According   to   the  latest  researches  of   the   Geophysical 
Laboratory,    the   essential   constituents   of   a   cement   are   tri- 
calcium  silicate  and  tri-calcium  alumina te.     Figure  a  formula 
similar  to  Eckel's  rule  on  this  basis. 

c.  Compute  the  relative  amounts  of  slag  and  limestone  by 
this  new  rule,  assuming  a  cementation  index  equal  to  one. 

d.  Repeat  a  for  this  cement. 

Furnace  Charges.  An  important  duty  devolving  upon  the 
smelter  metallurgist  is  that  of  computing  the  furnace  charge  or 
"  burden."  This  operation  consists  in  assembling  information  as 
to  the  composition  and  relative  amounts  of  the  various  ores  avail- 
able, the  composition  of  the  fuel  and  flux  on  hand,  and  in  combin- 
ing these  various  substances  at  the  charging  floor  so  that  they 
shall  issue  from  the  furnace  in  the  form  of  a  metallic  material  con- 
taining practically  all  the  values,  and  of  a  slag  holding  the  waste 
substances  which  cannot  be  converted  into  a  gas  and  volatilized. 
(See  Mills,  "  Materials  of  Construction,"  pp.  277,  278.)  In  the 
case  of  a  blast  furnace,  the  composition  of  the  slag,  matte,  or 
metal  tapped  from  the  crucible  depends  not  only  upon  the  com- 
position of  the  ore,  but  also  to  a  large  extent  upon  the  tempera- 
ture and  atmosphere  existing  in  the  furnace;  that  is  to  say, 
upon  the  amount  and  kind  of  fuel  which  is  burned,  the  quantity 
and  temperature  of  the  air  blown  in,  and  the  speed  with  which 
the  charge  passes  thru  the  combustion  zone.  For  these  rea- 
sons, it  is  not  possible  to  predict  the  furnace  operation  a  priori, 
but  one  must  make  certain  assumptions  regarding  the  expected 
action  of  the  furnace,  borne  out  by  past  experience  with  its 
operation. 

Illustrative  Example.  The  method  may  best  be  illustrated 
by  a  particular  case.  Suppose  it  is  the  duty  of  a  reverberatory 
furnace  in  a  copper  works  (see  Mills,  "  Materials  of  Construc- 
tion," p.  551)  to  smelt  roasted  concentrates  or  calcine,  (v.  p. 
13)  of  the  following  composition: 


ELEMENTARY  METALLURGICAL  CALCULATIONS      263 

Cu 9.9  per  cent 

SiO2 21.5 

FeO 40.5 

S 8.9 

A12O3 6.1 

CaO 5.0 

and  flue  dust  recovered  from  the  smoke  pipes  and  dust  chambers 
containing: 

Cu 8.1  per  cent 

Si02 25.3 

FeO 27.5 

S 15.8 

A12O3 :...   7-7 

CaO 1.3 

The  relative  amounts  of  these  two  materials  available  is  deter- 
mined by  the  production  of  the  allied  smelter  departments,  and 
for  the  purposes  of  this  problem  may  be  expressed  as  follows: 
For  every  70  Ib.  of  calcine  smelted,  30  Ib.  of  flue  dust  must  also 
be  charged.  A  small  but  unknown  amount  of  limestone,  which 
may  be  called  X  pounds,  will  be  added  to  bring  the  slag  to  the 
proper  composition.  The  composition  of  the  limestone  avail- 
able is: 

SiO2 5.6  per  cent 

FeO 0.7 

A1203 0.6 

CaO 50.3 

Past  experience  with  the  operation  of  these  furnaces  smelting 
calcine  and  flue  dust  will  indicate  the  production  of  a  molten 
alloy  of  iron  and  copper  sulfides,  called  "  matte,"  of  approx- 
imately the  following  composition: 

Cu 30  per  cent 

Fe 37 

S..  ..26 


264  APPENDIX  A 

and  that  96  per  cent  of  the  copper  charged  will  be  recovered  in 
this  matte,  the  remaining  4  per  cent  being  lost  in  the  slag  or 
by  dusting.  The  weight  of  the  matte  produced  can  be  imme- 
diately computed. 

Copper  from  calcine     =  9.9  per  cent  of  70  Ib.  =  6.93  Ib. 

Copper  from  flue  dust  =  8.1  per  cent  of  30  Ib.  =  2.43  Ib. 


Total  copper  charged  9 . 36  Ib. 

Total  copper  recovered  =  96  per  cent  of  9.36  Ib.  =  8 . 99  Ib. 

Weight  of  matte  at  30  per  cent  Cu =—  =  29 . 95  Ib. 

The  amount  of  the  iron  oxide  required  to  furnish  the  iron  for 
the  matte  should  also  be  computed  as  follows: 

Iron  required  for  matte  =37  per  cent  of  29.95  Ik.  =  n  .08  Ib. 
Iron  oxide  to  furnish  this  iron  =  — '—  X 1 1 .08  =  14 . 26  Ib. 

The  above  procedure  for  obtaining  the  weight  of  the  matte  i? 
much  superior  to  the  oft-recommended  scheme  of  assuming  that 
all  the  sulfur  charged  to  a  reverberatory  furnace  will  enter  the 
matte  primarily  as  Cu2S,  while  any  excess  sulfur  will  enter  in 
combination  with  iron  as  FeS.  This  is  an  unsafe  assumption, 
however,  for  sulfur  is  such  a  volatile  element  that  even  in  the 
reverberatory,  which  is  ordinarily  run  with  a  neutral  atmos- 
phere as  a  simple  melting  furnace,  a  large  and  uncertain  amount 
of  the  sulfur  is  eliminated  in  the  smoke. 

A  balance  of  the  materials  may  then  be  constructed  as  follows: 

MATERIALS  BALANCE 

Charges  To  29.95  Ib.  Matte  To  Slag                       To  Gas 
70  Ib.  calcine: 

Cu         9.9  per  cent  6 . 93  Ib.  Cu 

SiO2      21.5  iS.oslb.  SiOa 

FeO     40.5  n.oSlb.  Fe  14. 09  Ib.  FeO 

S            8.9  6.23lb.  S 

A12O3      6.1  4.27lb.  A12O2 

CaO       5.0  3. 50  Ib.  CaO 


ELEMENTARY  METALLURGICAL  CALCULATIONS      265 

Charges  To  29.95  lb.  Matte  To  Slag  To  Gas 

30  lb.  flue  dust: 

Cu         8.1  per  cent  2 . 43  lb.  Cu 

SiO2      25.3  7 . 59  lb.  SiO2 

FeO      27.5  8.25lb.  FeO 

S          15.8  i.s61b.  S  6.37lb.  SO2 

A12O3      7.7  2. 3 ilb.  A12O3 

CaO       1.3  o.39lb.  CaO 

X  lb.  limestone: 

SiO        5.6  per  cent  0.056^  lb.  SiO2 

FeO       0.7  o.oo7Xlb.  FeO 

A12O2      0.6  o .  oo6X  lb.  A12O3 

CaO     50.3  o.503Xlb.  CaO 

We  will  assume  for  the  purposes  of  computation  that  the 
various  slag-forming  constituents  unite  to  form  a  slag  which  is 
essentially  a  ferrous  silicate  where 

acid  :  base  =  47. 5  per  cent  :  52.5  per  cent. 

In  this  case  alumina  will  be  regarded  as  an  acid  capable  of 
replacing  SiC^,  molecule  for  molecule,  while  CaO  will,  in  like 
manner,  be  figured  to  its  equivalent  in  FeO.  Tabulate  the  slag 
constituents  as  follows: 


ACID 

BASE 

SiO2 

A1203 

FeO 

CaO 

From  calcine.  .  . 

•    I5-05 

4.27 

14.09 

3-50 

Flue  dust  

•     7-59 

2.31 

8.25 

0-39 

Limestone  .  .  . 

o  .  056^ 

o.oo6Z 

O.OO7.X' 

0.503^ 

Total  ......  22.64+0.056^  6.58+0.006^  22.34+0.007^"  3.89+0.503^ 


Total  acid  =  Si02  +--  A12O3      Total  base  =  FeO  +         CaO 

102.2  56.1 

=  26.52  +0.060  X  =27.32+0.651  X. 

Acid     .475     26.52+0.060^ 
By  hypothesis,  =  —  =_tl^  =  —  2  —  \  - 
'Base     .525     27.32+0.651^' 

Whence  ^  =  3.4  lb.  limestone. 

To  suit  the  conditions  of  the  problem,  the  charge  would  be 
made  up  in  the  proportion  of 


266  APPENDIX  A 

Calcine 70     Ib. 

Flue  dust 30     Ib. 

Limestone 3.4  Ib. 

The  mixture  is  practically  self-fluxing  without  the  lime  rock. 
Indeed,  the  roasting  practice  (page  13)  is  so  regulated  that  all 
the  iron  not  needed  to  form  a  matte  will  be  oxidized  from  the 
sulfide  condition  so  that  it  will  actually  go  into  the  slag  as  a  base, 
thus  replacing  the  CaO  as  much  as  possible.  A  longer  and  more 
perfect  roast  could  have  made  a  matte  with  less  iron  and  cor- 
respondingly higher  copper,  when  the  slag  would  absorb  the 
excess  iron.  However,  economic  conditions  will  govern  such 
factors  as  the  time  and  degree  of  roasting,  grade  of  matte  (that 
is,  its  copper  content),  and  the  silicate  degree  of  the  slag.  The 
student  will  notice  that  in  copper  smelting,  the  iron  contained 
in  the  ore  is  regarded  as  an  impurity,  is  eliminated  in  the  slag, 
and  wasted;  while,  in  iron  smelting,  on  the  contrary,  every 
effort  is  made  to  save  the  iron,  recovering  it  as  metal. 

In  general,  then,  the  solution  of  problems  relating  to  furnace 
charges  may  best  be  effected  by  constructing  a  balance  sheet 
showing  the  origin  and  expected  disposition  of  each  constituent 
making  up  the  total  burden.  Economic  considerations  will  fix 
the  relative  proportions  of  the  various  ores  available,  and  the 
analysis  of  the  metallic  product.  To  obtain  this  result,  former 
experience  will  indicate  the  required  amount  of  fuel  and  the  ratio 
of  acid  to  base  in  the  slag  Algebraic  solution  will  be  relied  upon 
to  obtain  the  unknown  amount  of  flux  or  to  evaluate  other  vari- 
ables existing  in  the  problem. 

Queries,     a.  A  hematite  ore  of  the  following  composition: 

H20 9.8  per  cent 

SiO2 10.2 

A1203... 3-5 

Fe2O3 75.5 

MnO 1.0 

is  to  be  smelted  in  a  blast  furnace  producing  a  pig  with 


ELEMENTARY  METALLURGICAL   CALCULATIONS      267 

Fe 94.5  per  cent 

Mn 0.5 

c 3.9 

Si i.i 

using  i  Ib.  of  coke  of  the  following  composition  for  every  pound 
of  pig  iron  produced : 

SiO2 5-4  per  cent 

CaO 4.4 

H2O i.i 

C 87.9 

FeO 1.4 

A  "  neutral  slag "    (essentially  a  lime  silicate  with  the  ratio 

acid     47.5  per  centA  . 

-  =—  -    is  required  for  this  particular  pig  iron,  and 

base     52.5  per  cent/ 

is  attained  by  charging  limestone  of 

SiO 5.2  per  cent 

MgO 4-8 

CaO 47.4 

CO2 ...42.6 

Assuming  that  all  the  Fe2Os  of  the  ore  will  be  reduced  and  fur- 
nish the  iron  for  the  pig  iron,  while  the  iron  oxide  in  the  coke 
ash  will  enter  the  slag,  figure  the  weight  of  ore  required  to  pro- 
duce 100  Ib.  of  pig  iron. 

b.  Construct  a  balance  sheet  of  the  furnace  charge,  repre- 
senting the  amount  of  limestone  charged  by  X. 

c.  Compute  the  pounds  of  limestone  needed  for  100  Ib.  of 
pig  iron.     Regard  AkOa  as  an  acid,  and  equal,  molecule  for 
molecule,  to  SiO2;   and  compute  the  other  oxides  to  their  CaO 
equivalent. 

d.  The  silicon  and  manganese  of  the  pig  iron  may  be  regarded 
as  being  reduced  by  carbon,  forming  CO.     How  much  C  is  used 
in  this  manner,  and  how  much  enters  the  pig  iron  as  such? 

e.  Air  blown  in  at  the  tuyeres  burns  the  balance  of  the  C 


268  APPENDIX  A 

in  the  coke  to  CO.  Assuming  dry  air  at  standard  conditions, 
and  blowing  in  10  per  cent  excess,  how  much  air  must  be  charged? 

/.  Assume  that  all  of  the  iron  oxide  has  been  reduced  by  CO; 
that  the  CO2  of  the  limestone  and  all  moisture  has  been  driven 
off  undecomposed;  what  is  the  percentage  composition,  by 
volume,  of  the  gas  at  the  top  of  the  furnace?  How  many  cubic 
feet  of  this  gas,  measured  at  standard  conditions,  would  be 
formed  per  100  Ib.  of  pig  iron  produced? 

g.  How  much  heat  is  absorbed  in  reducing  the  elements  con- 
tained in  the  pig  iron?  How  much  heat  could  be  evolved  by 
the  total  combustion  of  the  carbon?  What  is  the  heat  efficiency 
of  the  furnace  on  this  basis? 

h.  What  percentage  of  the  total  calorific  power  of  the  coke 
is  recovered  in  the  top  gas? 


APPENDIX  B 


FOUNDRY  PRACTICE  * 

Introductory.  Castings,  as  used  in  the  building  and  manu- 
facture of  machines  and  metallic  equipment,  are  commonly 
made  of  iron,  steel,  aluminum,  brass  and  bronze.  Castings  of 
iron,  however,  are  the  least  expensive  in  proportion  to  strength, 
and  their  production  constitutes  the  largest  part  of  the  foundry 
business.  And  since  the  methods  of  producing  iron  castings 
are  quite  similar  to  those  for  the  other  materials  just  mentioned, 
the  differences  being  largely  metallurgical  in  character,  we  shall 
confine  our  present  study  to  the  practice  of  the  average  iron 
foundry. 

This  study  is  of  importance  to  every  engineer,  because  while 
he  may  not  be  concerned  with  the  direct  production  of  castings, 
he  is  sure  to  encounter  their  design,  purchase,  or  use,  and  it  is 
therefore  necessary  that  he  understand  the  basic  principles  of 
molding  on  which  their  design,  cost,  or  use  must  depend. 

The  cost  of  a  casting  is  proportional  to  three  values : 

a.  The  amount  and  nature  of  the  metal  and  materials  used. 

b.  The  time  and  labor  required  to  make  the  mold. 

c.  The  difficulty  of  securing  a  casting  which  is  free  from 
defects. 

The  amount  of  metal  used  has  the  greatest  effect  on  the  cost 
in  the  case  of  large  castings.  A  careful  design  will  require  the 


*  One  of  the  coordination  papers  in  use  at  the  University  of  Cincinnati,  by  Max 
B.  Robinson,  M.E.,  Professor  of  Mechanical  Engineering,  University  of  Akron, 
formerly  Instructor  of  Coordiration  at  the  University  of  Cincinnati. 

269 


270  APPENDIX  B 

minimum  of  metal  consistent  with  the  necessary  strength,  rigidity 
and  mass,  according  to  principles  of  Strength  of  Materials  and 
Mechanics.  For  example,  economical  specifications  will  not 
call  for  steel  or  aluminum  where  cast  iron  would  serve.  Neither 
would  they  call  for  an  expensive  grade  of  gray  iron,  when  white 
iron  would  satisfy  the  requirements. 

The  time  and  labor  required  to  make  this  mold  can  be  greatly 
increased  by  unintelligent  or  careless  designs.  In  fact,  designs 
actually  impossible  to  produce  are  not  uncommon,  but  the  piece 
could  easily  be  constructed  by  paying  heed  to  certain  unalterable 
limitations  of  molding.  It  should  be  remembered  that  very 
slight  changes  in  design  can  alter  the  entire  method  of  molding, 
and  the  consequent  cost  of  production.  Attention  will  be  called 
to  points  wherein  the  design  depends  upon  methods  of  molding, 
and  vice  versa. 

The  third  variable,  mentioned  above,  namely,,  the  risk  of 
securing  an  unsound  casting,  will  be  discussed  under  "  the 
Defects  of  Castings  "  on  page  284.  Many  of  these  are  caused 
by  faulty  design. 

Molding.  In  general,  a  casting  is  made  by  pouring  molten 
metal  into  a  mold,  the  mold  being  made  of  refractory  material 
such  as  sand  or  loam,  its  interior  shape  determining  the  shape  of 
the  poured  metal  after  solidifying.  Some  molds  are  made  of 
metal  and  produce  "  die-castings,"  but  they  will  not  be  consid- 
ered here,  as  their  use  is  rather  specialized. 

Most  commonly,  the  cavity  in  the  mold  is  shaped  by  "  ram- 
ming up  "  molding  sand  inside  a  flask  and  around  a  wood  or 
metal  pattern,  which  becomes  embedded  in  the  sand,  and  which, 
when  removed,  leaves  a  cavity  of  the  required  shape.  An 
extremely  simple  form  of  mold,  for  example,  would  be  that  for 
making  a  rectangular  block,  4X8  in.,  and  2  in.  thick,  using  a  one- 
piece  pattern.  This  would  be  molded  entirely  within  the  drag, 
or  lower  half  of  the  flask  containing  the  mold,  since  it  has  a  flat 
top  and  straight  sides  and  can,  therefore,  be  easily  removed.  A 
pattern  such  as  the  above  is  called  a  "  flat-back,"  and  the  order 
of  operations  in  molding  it  would  be  as  follows: 


FOUNDRY  PRACTICE 


271 


1.  Place  the  mold  board  on  the  bench,  the  cleats  extending 
away  from  the  molder  to  prevent  tipping  when  turning  over. 

2.  Place  the  pattern  on  the  mold  board,  top  side  down. 

3.  Place  the  drag  upside  down  over  the  mold  board  and  pat- 
tern, with  the  pins  extending  downwards  on  either  side  of  the 
board. 

4.  Sift  some  facing  sand  over  the  pattern  until  it  is  covered, 
using  a  fine  riddle. 


FIG.  55.- — Section  thru  a  Mold  Containing  a  Rectangular  Pattern. 


A  =  bottom  board. 

B  =  drag. 

C  =  cope. 

D  =  parting,  or  joint. 


E  =  pattern. 

F  =  sprue. 

G=gate. 

H  =  pouring  basin,  or  skim  gate. 


5.  Tuck  the  riddled  sand  around  the  edge  of  the  pattern  with 
the  fingers. 

6.  Shovel  the  drag  full  of  old  sand. 

7.  Ram  around  the  inside  edge  of  the  flask  with  the  peen  or 
sharp  edge  of  the  rammer,  butt  end  inclining  toward  the  center 
of  the  flask. 

8.  Butt-ram  entire  surface,  using  more  sand  if  necessary  to 
fill  the  flask. 

9.  Scrape  off  any  surplus  sand  with  a  "  strike." 


272  APPENDIX  B 

10.  Throw  a  little  loose  sand  on  the  flat  surface. 

11.  Place  the  bottom  board  on  the  drag,  and  rub  it  to  a  firm 
bearing. 

12.  "  Roll  over  "  the  drag,  bringing  the  pattern  up. 

13.  Remove  the  match  plate  or  mold  board. 

14.  Brush  the  surface  with  a  soft  brush,  or  use  a  bellows. 

15.  Sprinkle  parting  sand  over  the  sand  to  separate  the  cope 
and  drag  portions  of  the  mold. 

1 6.  Blow  the  excess  of  parting  sand  from  the  surface  of  the 
pattern.     (In  case  a  two-piece  pattern  were  used,  the  upper  half 
would  here  be  placed  on  the  lower  half.) 

17.  Place  the  cope  on  the  drag,  with  pins  fitting  in  to  ears  on 
the  other  half. 

18.  Place  a  "  gate  stick  "  in  position,  extending  a  slight 
distance  into  the  drag. 

19.  Repeat  operations  4  and  9  in  the  cope. 

20.  Prick  vent  holes  where  needed. 

21.  Remove  the  gate  stick  from  the  sand. 

22.  Lift  the  cope  from  the  drag,  and  place  it  at  one  side, 
bottom  up. 

23.  Smooth  off  any  rough  places  appearing  on  the  sand  sur- 
faces with  a  slick  or  other  hand  tools. 

24.  Bevel  the  gate  hole  at  the  joint,  and  ream  the  top  into  a 
bell-shape  for  pouring,     (In  some  cases  a  "  skim  gate  "  would 
be  advisable.     H,  Fig.  55.) 

25.  Withdraw  the  pattern,  using  a  draw  nail  and  rapping  iron. 

26.  Cut  a  sprue  from  the  gate  hole  to  the  mold  in  the  top 
surface  of  the  drag,  using  a  sprue  cutter. 

27.  Finish  by  hand  any  imperfections  on  the  surface  of  the 
mold. 

28.  Replace  the  cope  on  the  drag. 

29.  Place  the  mold  in  position  to  be  poured. 

30.  Unlock  and  remove  the  flask. 

31.  Place  a  flat  cast-iron  weight  on  the  cope  to  hold  the  sand 
down  and  to  prevent  a  "  run-out." 

The  skill  required  of  the  molder  in  performing  the  above  oper- 


FOUNDRY  PRACTICE  273 

ations  lies  mainly  in  ramming,  in  hand  finishing  and  retouching, 
and  in  handling  the  finished  parts.  The  necessary  skill  increases 
in  proportion  to  the  complexity  of  the  pattern.  Correct  ram- 
ming is  largely  a  matter  of  experience,  the  hardness  with  which 
the  sand  is  rammed  depending  on  the  size  of  the  mold,  the  size, 
"  temper  "  and  composition  of  the  sand,  and  the  weight  of  the 
casting.  Ramming  too  hard  will  cause  blowholes,  since  it  re- 
duces the  porosity  of  the  sand  and  gas  cannot  escape  from  the 
mold.  Ramming  too  loose  will  allow  the  sand  to  sink  or  bulge 
out  under  the  pressure  of  the  iron,  and  a  swelled  casting  is  the 
result;  or,  sand  may  be  washed  from*  the  face  of  the  mold, 
forming  scales  or  sandholes  on  the  finished  work.  The  bottom 
of  the  mold  and  the  joint  must  sometimes  be  rammed  harder 
than  the  other  parts  because  the  former  must  stand  the  weight 
of  the  metal,  and  the  latter  is  exposed  to  much  handling.  Beyond 
sufficient  hardness  to  maintain  proper  shape,  the  risk  of  losing 
the  casting  increases  with  the  hardness  of  the  ramming.  The 
ramming  tool  should  never  strike  nearer  than  i  in.  to  the  pattern, 
else  a  hard  spot  in  the  sand  will  be  formed  which  may  cause  a 
"  scab  "  on  the  casting. 

Retouching  is  largely  a  matter  of  the  deft  use  of  hand  tools. 
All  slicking  should  be  lightly  done,  else  scabs  will  be  caused. 
Care  must  also  be  taken  not  to  get  the  sand  too  wet.  The  cope 
should  always  be  finished  before  the  drag,  because  should  it  be 
spoiled  in  any  way,  the  drag  still  contains  its  pattern  and  a  new 
cope  can  at  once  be  made. 

In  commercial  work,  but  few  castings  are  as  simple  to  mold 
as  the  rectangular  pattern  illustrated  above,  irregularities  in 
shape  greatly  complicating  the  molding  operations.  In  order 
that  the  pattern  may  be  withdrawn  from  the  sand  without  break- 
ing away  any  of  the  surface  of  the  parting,  most  patterns  not 
having  a  flat  top  surface,  or  not  having  every  horizontal  section 
as  great  or  greater  in  width  than  every  horizontal  section  below 
it,  must  be  molded  partly  in  the  cope,  instead  of  wholly  in  the 
drag.  A  pattern  having  a  horizontal  section  less  in  width  than 
that  of  sections  both  above  and  below  it,  as  a  sheave  pulley, 


274 


APPENDIX  B 


Fig.  56,  requires  a  three-part  flask,  or  else  a  two-part  flask  and  a 
false  cheek.  Pulleys  with  more  than  one  sheave  require  as  many 
cheeks  as  there  are  sheaves. 

Molding  is  also  complicated  by  setting  of  "  gaggers  "  and 
"  soldiers  "  to  support  overhanging  bodies  of  sand,  by  the  fre^ 
quent  necessity  for  drying  the  mold  or  skin-drying  the  surfaces, 
by  the  use  of  blackings  and  special  facings,  by  special  forms  ol 
pouring  gates,  by  the  placing  of  shrinkheads  and  risers,  and  b)J 
the  placing  of  cores.  Oftentimes  patterns  must  be  placed  with  a 
certain  surface  on  the  bottom  in  order  to  receive  the  purest  iron 
(impurities  rise  to  the  top),  but  if  this  is  not  required,  the  pattern 
is  placed  in  whatever  position  will  allow  the  mold  to  be  made  by 


FIG.  56.— Sheave  Pulley  Pattern  in  Three-part  Flask. 

the  simplest  method.  This  requires  good  judgment  on  the  part 
of  the  molder. 

To  illustrate  some  of  the  variations  of  molding  from  the  order 
of  operations  on  page  271  consider  the  molding  of  a  cylinder 
6  in.  in  diameter  and  12  in.  long.  This  cylinder  can  be  molded 
in  several  ways,  each  of  which  illustrates  a  molding  method  in 
common  use,  since  most  shapes  are  modifications  or  combinations 
of  cylinders  and  rectangles.  Where  several  methods  are  possible 
such  considerations  as  the  weight  of  the  casting,  the  equipment 
at  hand,  the  finish  required,  and  the  number  of  one  kind  required 
will  determine  the  best  method  to  use  for  an>  given  pattern. 

Probably  the  simplest  way  of  molding  the  cylinder  on  its 
side  is  by  the  "  split  pattern  "  method,  in  which  the  cylindrical 
pattern  is  split  into  upper  and  lower  halves,  pins  extending  down 


FOUNDRY  PRACTICE 


275 


from  the  upper  half  engaging  holes  in  the  lower  half.  The  half 
of  the  pattern  which  goes  in  the  drag  is  placed  flat  on  the  mold 
board,  and  the  drag  rammed  up  as  in  operations  i  to  13,  page  271. 
After  turning  over  the  drag,  the  upper  half  of  the  pattern  is 
placed  on  the  lower,  held  in  position  by  the  pins,  and  the  mold 
is  finished  as  in  operations  1 7  to  3 1 . 

Another  common  method  of  molding  this  cylinder  is  the 
"  bedding  in  "  method.  The  drag  is  placed  on  the  mold  board 
in  an  upright  position,  rammed  full,  struck  off  even  with  its  top 
edge,  and  the  one-piece  pattern  is  then  bedded  in  to  its  parting 
line,  Fig.  57,  by  scooping  out  a  sufficient  space,  tucking  the  sand 
firmly  around  the  sides  and  ends  of  the  pattern,  and  patching 


FIG.  57.— Pattern  that  is  "  Bedded  In." 

the  broken  parting  by  hand.  This  method  is  crude,  but  it  saves 
turning  the  drag,  and  is  much  used  in  England  where  heavy 
iron  flasks  are  the  rule. 

Another  common  method  of  bringing  the  parting  line  of  the 
pattern  to  a  level  with  the  joint  between  the  cope  and  drag,  is 
to  place  wedges  between  the  mold  board  and  the  edges  of  the 
drag,  holding  it  up  to  a  height  equal  to  that  which  the  pattern 
is  to  project  into  the  cope.  The  pattern  is  then  placed  in  posi- 
tion on  the  mold  board,  Fig.  58,  and  the  drag  rammed  up.  The 
drag  is  turned  over,  the  excess  sand  on  the  top  struck  off  and  the 
parting  made.  The  disadvantage  of  this  method  lies  mainly  in 
the  extra  work  required  in  making  a  good  parting. 

The  method  of  "  coping  down  "  is  also  frequently  used.  In 
this,  the  drag  is  rammed  up  with  the  pattern  in  place  exactly  as 


276 


APPENDIX  B 


in  operations  i  to  14,  page  271.  To  permit  the  pattern  to  be 
withdrawn,  the  sand  is  then  cut  away  from  around  the  pattern 
down  to  its  exact  center,  its  parting  line,  making  as  gradual  a 
slope  as  possible,  as  shown  in  Fig.  59.  The  surface  is  slicked, 


FIG.  58.—"  Wedging  Up." 


FIG.  59.—"  Coping  Down." 

A,  section  thru  drag,  pattern  in  position. 

B,  side  of  cope. 

parting  sand  dusted  on,  and  the  cope  rammed  as  usual.  This 
method  leaves  a  body  of  sand  hanging  down  from  the  cope,  hence 
its  name. 

Molding  with  a  Match.     The  fifth  method  of  molding  the 
cylinder  employs  the  use  of  a  "  match,"  and  is  commonly  used 


FOUNDRY  PRACTICE  277 

for  patterns  with  an  irregular  top  surface,  which  cannot  be  split, 
and  yet  must  lie  partly  in  the  drag  and  partly  in  the  cope.  A 
match  is  a  mold  used  as  a  mold  board  into  which  the  pattern 
fits  up  to  its  parting  line.  The  operations  of  ramming  the  drag 
and  cope  are  identical  with  those  already  listed.  Matches  are 
made  of  green  sand,  oil  sand,  plaster  of  Paris,  or  metal.  A 
green  sand  match  is  used  when  only  a  few  castings  are  needed. 
When  desirable  to  keep  the  match  for  a  period  of  time,  an  oil- 
sand  match  is  made,  and  for  permanent  use,  it  should  be  made  of 
plaster  of  Paris.  A  match  is  made  in  a  shallow  frame  the  size 
of  the  flask  to  be  used.  If  but  one  casting  is  required,  a  tem- 
porary match  or  "  upset  "  is  made  by  filling  the  frame  with  loose 
sand  and  then  "  bedding  in  "  the  pattern  the  same  amount  that 
it  is  later  to  project  into  the  cope.  The  sand  should  be  tucked 
and  rammed  around  the  pattern  merely  enough  to  hold  the  latter 
in  place.  The  drag  is  then  rammed  on  top  of  the  upset,  and  the 
cope  on  top  of  the  drag,  as  in  preceding  cases. 

When  a  green-  or  oil-sand  match  is  wanted  for  subsequent 
molds,  an  upset  is  made  first  and  the  drag  rammed  on  the 
upset.  The  drag  is  rolled  over  and  the  sand  knocked  out  of 
the  upset,  which  is  placed  bottom  side  up  on  the  drag,  the  pat- 
tern still  being  in  the  drag  and  projecting  up.  The  upset  is  then 
rammed  the  same  as  a  cope,  enabling  the  sand  to  be  packed  from 
the  side  which  is  to  form  its  bottom,  making  a  smooth  parting 
between  the  upset  and  the  drag.  When  so  rammed,  the  upset 
becomes  either  a  green-sand  or  an  oil-sand  match  depending  on 
whether  water  or  linseed  oil  has  been  mixed  with  the  sand  as  a 
binder.  Oil  matches  are  hardened  by  baking  in  core  ovens. 
After  ramming  the  match,  the  drag  is  ready  to  be  used  for  ram- 
ming the  cope. 

Molding  with  Sweeps.  Molds  for  circular  boiler  fronts,  tank 
heads,  pulley  and  flywheel  rims,  large  cylinders  and  other  purely 
circular  shapes  can  be  made  without  a  pattern  by  the  aid  of  a 
"  sweep."  This  is  often  of  economic  importance  when  but  one 
or  a  few  castings  of  a  kind  are  wanted. 

The  "  sweep  "  consists  of  a  board  having  its  edge  or  end 


278  APPENDIX  B 

profiled  to  correspond  with  the  desired  contour  of  the  surface  of 
the  casting,  and  is  attached  to  a  "  sweep  finger  "  which  rotates 
about  a  vertical  spindle  firmly  set  in  a  block  in  the  floor.  The 
mold  is  shaped  by  turning  the  board  around  the  vertical  spindle 
as  a  center,  its  edge  or  end  imparting  the  desired  contour  to  the 
surfaces  of  the  material  of  which  the  mold  is  made.  Castings 
that  are  irregular  in  shape  can  be  partially  made  in  this  manner, 
and  the  balance  of  the  mold  made  with  smaller  "  pattern 
pieces." 

Many  molds  are  swept  in  loam  instead  of  in  sand,  the  loam 
being  swept  against  a  roughly  constructed  brick  backing  which 
takes  the  place  of  a  flask.  The  mold  is  then  baked,  causing  the 
loam  to  adhere  firmly  to  the  brick. 

Molding  Sand.  Molding  sand  must  possess  qualities  which 
will  enable  it  to  be  tempered  and  to  retain  a  definite  shape  in  the 
mold.  It  must  resist  fusion,  must  have  permeability  to  permit 
the  ready  escape  of  gases,  and  must  be  capable  of  being  retem- 
pered  and  used  a  number  of  times.  These  qualities  depend  upon 
its  chemical  composition  and  physical  constitution.  Sands  from 
different  localities  possess  these  qualities  to  different  degrees. 
Also  different  classes  of  work  require  different  sands.  The 
coarseness  and  the  constituency  required  for  any  given  work 
depend  upon  the  size  and  weight  of  the  castings,  upon  the  tern-1 
perature  of  the  molten  metals,  upon  the  length  of  time  it  will  take 
the  metal  to  cool,  upon  the  degree  of  finish  desired,  etc.  Sand 
as  it  comes  from  the  pit  must  be  "  burned  "  to  destroy  vegetable 
and  animal  life.  The  color  of  sand,  which  is  reddish-yellow  before 
use,  changes  to  black  after  use.  (When  sand  becomes  worn 
out,  that  is,  loses  its  bond  or  cohesion  thru  repeated  use,  it 
should  be  replaced.)  Sand  for  steel  castings  must  be  more 
refractory  than  sand  for  cast  iron,  due  to  the  higher  temper- 
atures involved.  Sand  for  brass  work  need  be  less  so. 

Facings.  Oftentimes  sand  cannot  be  used  for  the  surface  of 
a  mold  without  further  treatment,  due  to  its  tendency  to  fuse 
with  the  iron  under  prolonged  heat,  and  also  due  to  its  inability 
to  form  as  smooth  or  finished  a  surface  as  desired  on  the  casting 


FOUNDRY  PRACTICE  279 

of  the  mold.  A  facing  material  then  becomes  necessary.  It  is 
either  mixed  with  the  sand  that  is  used  next  to  the  pattern,  or 
painted  or  dusted  on  the  surface  of  the  mold,  or  both.  Different 
facings  are  are  used  for  different  purposes.  Common  lacings  are 
sea-coal,  which  is  a  special  grade  of  bituminous  coal,  ground,  and 
screened  to  the  required  fineness;  plumbago,  which  is  a  form  of 
graphite;  coke  and  charcoal  "  blacking  "  compounds;  talc  or 
soapstone;  and  gas-house  carbon.  Certain  mixtures  and  cer- 
tain amounts  of  the  above  are  used,  depending  upon  the  temper- 
atures dealt  with,  the  kind  of  sand  used,  the  duration  of  the 
intense  heat,  whether  the  mold  is  skin-dried,  dry-sand,  or  green 
sand,  and  the  finish  required  on  the  surface  of  the  casting. 

Cores.  Cavities  in  castings  are  formed  by  cores,  usually 
made  at  the  bench  with  a  special  grade  of  sand  called  "  core 
sand."  This  is  mixed  with  a  "  binder,"  and  is  molded  to 
shape  in  wood  or  metal  core  boxes,  the  interiors  of  which  are 
shaped  so  as  to  produce  the  required  forms.  Cores  are  some- 
times built  upon  special  forms  or  drums.  The  cores  are  then 
baked  in  "  core-ovens  "  to  render  them  hard  and  to  fix  their 
shape.  Core  sand  has  different  qualities  from  molding  sand,  and 
selection  of  the  right  sand  is  important.  The  binders  commonly 
used  are  wheat  flour,  rye  meal,  powdered  rosin,  linseed  oil,  and 
glue,  prepared  in  various  ways,  and  used  in  various  proportions. 
Cores  must  be  vented  to  allow  the  ready  escape  of  gases.  Wax 
tapers,  which  melt  and  leave  vent  holes  when  the  core  is  baked, 
are  often  inserted  when  molding  the  core.  These  are  used 
especially  in  thin  cores,  and  where  it  would  otherwise  be  difficult 
to  lead  a  vent  around  a  corner,  as,  for  example,  in  locomotive 
cylinder  ports. 

The  location  of  cores  in  the  mold  is  usually  determined  by  the 
"  core  prints  "  on  the  pattern,  where  they  are  usually  painted 
red  or  black.  When  set  in  molds,  cores  must  be  supported  on 
the  bottom,  sides  and  top,  either  by  core  prints  or  by  chaplets. 
Chaplets  come  in  various  forms  to  fit  against  flat,  convex,  or. 
concave  surfaces  and  for  both  light  and  heavy  work.  Some 
types  come  in  assorted  sizes,  and  some  types  are  adjustable  to 


280  APPENDIX  B 

suit  any  required  height.  Most  chaplets  are  tinned  to  fuse 
readily  into  the  molten  iron. 

Different  Classes  of  Molds.  Green-sand  Molds.  These  are 
molds  made  from  moist  and  tempered  sand  and  not  dried  by 
artificial  means.  Most  small  castings  are  molded  in  green  sand. 

Dry-sand  Molds.  Where  a  very  strong  mold  is  required, 
either  to  resist  erosion  by  the  iron  when  pouring,  or  to  maintain 
its  shape  against  a  high  fluid-pressure,  the  sand  is  mixed  with  a 
binding  material  and  the  finished  mold  is  baked  in  a  mold  oven. 
This  process  is  similar  to  that  used  in  baking  cores.  Examples 
of  work  cast  in  these  molds  are :  steam  and  gas-engine  cylinders, 
air  compressor  and  hydraulic  cylinders,  printing-press  cylinders 
and  rolls,  anvil  blocks,  engine  beds  and  similar  heavy  castings. 

Skin-dried  Molds.  These  molds  are  dry  on  the  surface  only, 
being  a  compromise  between  green-sand  molds  and  dry-sand 
molds.  They  are  made  of  green  sand  without  a  binder,  and 
the  drying  is  effected  by  gas  or  oil  flames  either  placed  in  posi- 
tion or  played  on  the  different  surfaces  by  workmen.  Most 
medium  and  heavy  molds  which  do  not  require  a  complete  dry- 
ing are  skin  dried,  the  process  materially  strengthening  the  sand 
walls. 

Bench  Molds.  These  are  small  molds  whose  size  makes  it 
most  convenient  to  mold  them  on  a  bench. 

Floor  Molds.  The  majority  of  molds  are  made  in  flasks 
which  rest  on  the  floor.  In  large  floor  work,  the  copes  contain 
ribs  and  cross  ribs,  or  "  chucks,"  for  the  purpose  of  supporting 
the  large  areas  of  sand  contained  in  them.  These  ribs  are  cut 
away  where  it  is  necessary  to  allow  patterns  to  project  into  the 
cope.  Care  must  be  taken  in  placing  the  pattern  to  see  that  it 
does  not  come  too  near  such  ribs.  In  floor  work,  where  it  is 
often  possible  to  mold  several  pieces  in  the  same  flask,  nicety 
of  judgment  is  required  in  determining  which  pieces  can  go 
together  in  this  manner. 

Pit  Molds.  Often  a  pit  dug  in  the  floor  serves  the  purpose  of  a 
drag,  the  cheek  and  cope  being  the  only  parts  of  the  flask  re- 
quired. This  saves  expense,  especially  in  extra  large  work.  If 


FOUNDRY  PRACTICE  281 

the  earth  is  too  damp,  a  permanently  dry  pit  may  be  constructed 
by  sinking  an  iron  tank  in  the  ground,  or  the  inside  of  the  pit 
may  be  cemented  or  lined  with  tar  paper. 

Machine-made  Molds.  Where  many  small  molds  are  required 
from  the  same  pattern,  or  where  there  is  difficulty  in  ramming 
the  same  or  in  removing  the  pattern  by  hand,  molding  machines 
are  often  employed.  See  under  the  heading  "  Molding 
Machines." 

Molding  Equipment.  Flasks.  Flasks  are  made  of  iron, 
steel  or  wood.  Iron  flasks  are  used  for  very  heavy  castings. 
These  are  made  so  as  to  be  interchangeable,  with  pin-holes  in 
their  flanges  bored  with  a  templet.  Iron  flasks  should  be 
ribbed  to  prevent  springing  from  the  pressure  of  the  iron  in  the 
mold.  There  should  be  ample  room  for  sand  between  the  pat- 
tern and  the  side  of  the  mold  not  only  to  avoid  heating,  but  to 
absorb  any  gases  which  are  evolved.  Trunnions  for  turning 
with  a  crane  should  be  made  of  steel  cast  into  sides  of  the  flask, 
rather  than  of  iron  cast  in  one  piece  with  the  flask.  Steel  flasks 
are  light  and  serviceable,  but  on  account  of  their  lightness,  heat 
up  rapidly  and  are  apt  to  warp  out  of  shape.  Wooden  flasks 
should  be  of  substantial,  thick  material,  as  they  are  subject  to 
burning  at  the  joints,  which  will  later  cause  run-outs. 

Molding  Machines.  Molding  machines  are  in  general  use 
on  light  and  medium  work  where  a  number  of  molds  are  to  be 
made  from  the  same  pattern.  The  common  machines  used  are 
the  Hand  Squeezer,  The  Power  Squeezer,  the  Split-pattern 
Machine,  the  Roll-over  Machine  and  the  Jarring  Machine. 

Where  the  ramming  time  is  the  largest  factor  in  the  making  of 
the  mold,  and  where  the  mold  is  thin,  one  of  the  squeezer 
machines  is  used.  But  as  a  squeezer  machine  packs  the  sand  by 
pressure  on  its  surface,  and  the  top  is  packed  harder  than  the 
bottom  it  is  not  as  well  adapted  to  deep  molds  as  the  jarring 
machine.  A  jarring  machine  in  which  the  .impact  of  the  mold  on 
the  table  is  absorbed  by  air  cushions  and  springs  within  the 
machine  itself,  instead  of  being  transmitted  to  the  surrounding 
floors  and  walls,  is  called  "  Shockless  Jarring  Machine." 


282  APPENDIX  B 

Where  a  mold  is  such  that  the  pattern  is  difficult  to  draw  by 
hand  without  injury  to  the  mold,  and  the  consequent  finishing 
time  is  the  largest  factor  in  the  making  of  the  mold,  either  a 
Split  Pattern  or  Rollover  Machine  is  used,  depending  on  the 
shape  of  the  pattern.  For  description  of  each  type  of  machine 
see  "  Foundry  Practice,"  by  Palmer. 

General  Foundry  Equipment.  Besides  the  molding  opera- 
tions, the  elements  of  foundry  work  involve : 

1.  The  handling  of  raw  and  finished  materials. 

2.  The  melting  and  pouring  of  the  metals. 

3.  The  cleaning  of  the  castings  after  they  have  cooled. 
The  equipment  necessary  for  the  foregoing  includes: 

1.  Suitable  cranes,  hoists  and  rigging  for  handling  the  raw 
materials,  molds,  ladles  and  the  finished  castings. 

2.  A  cupola  for  melting  the  iron,  with  equipment  for  fur- 
nishing a  suitable  air-blast,  and  ladles  for  distributing  iron  to  all 
parts  of  the  floor. 

3.  Rattlers  or  tumbling  barrels,  pickling  vats,  and  tools  for 
cleaning  the  castings  by  hand. 

Important  points  to  above  equipment  are  as  follows: 

Cranes.  The  old-fashioned  jib-cranes,  operated  by  a  hand 
winch,  limited  in  application,  and  useless  beyond  the  radius  of 
the  crane  arm,  have  been  displaced  by  the  traveling  crane  of 
either  the  hand  or  electric  type.  The  important  requirement  for 
a  satisfactory  crane,  aside  from  its  ability  to  safely  carry  the 
weight,  is  a  delicate  and  sensitive  control.  The  handling  of 
green-sand  molds  requires  gradual  stopping  and  starting,  with 
no  shocks,  and  the  safe  carrying  and  pouring  of  molten  metal 
demands  the  ability  to  operate  at  very  slow  speeds,  on  either  a 
light  or  heavy  load. 

Rigging.  The  rigging  required  depends  upon  the  class 
of  work  being  done,  and  generally  consists  of  chains,  slings, 
yokes,  etc. 

The  Cupola.  For  melting  iron,  one  of  two  types  of  furnaces 
may  be  used,  either  the  cupola,  or  the  reverberatory  or  air 
furnace.  The  more  common  cupola  is  an  upright  cylindrical 


FOUNDRY  PRACTICE  283 

shaft  furnace,  open  at  the  top  and  bottom,  and  lined  with  fire 
brick.  It  is  provided  with  a  charging-door  at  about  the  middle 
of  its  height.  There  are  "  tuyeres  "  near  the  bottom,  thru 
which  air  is  blown  which  consumes  the  fuel  charged  and  melts 
the  iron.  The  shell  is  formed  of  separate  rings  of  boiler-plate, 
with  angles  riveted  at  intervals  to  the  interior  to  support  the 
fire-brick  lining. 

The  cupola  shell  is  carried  on  a  cast-iron  bed-plate  ring  sup- 
ported by  cast-iron  legs.  The  opening  in  this  ring  is  tightly 
closed  during  operation  by  hinged  doors  which  are  allowed  to 
open  at  the  end  of  the  heat. 

Molten  iron  is  removed  just  above  the  bottom  thru  the 
"  tap-hole."  Slag  is  removed  thru  the  "  slag-hole  "  on  the 
opposite  side,  slightly  higher  than  the  tap-hole.  Cleaning  holes 
or  doors  on  each  side  of  the  wind  box  permit  removal  of  slag  or 
dirt  therefrom.  Peep-holes  opposite  each  tuyere  allow  the 
melter  to  judge  the  temperature  of  the  focus. 

The  space  in  the  cupola  constitutes  zones,  as  follows: 

1.  Crucible  zone,  or  hearth,  extending    from    the  bottom 
to  the  lower  row  of  tuyeres. 

2.  Tuyere   or   combustion    zone,   next    above,    where    the 
blast  comes  in  contact  with  and  burns  the  red-hot  coke.     Its 
upper  limit  depends  on  the  blast  pressure,  but  should  be  between 
15  in.  and  24  in.  above  the  tuyeres. 

3.  Melting  zone,  next  above,  which  is  about  7  in.  high. 

4.  The  "stack"  extending  from  the  melting  zone  to  the 
charging  door.     Its  function  is  to  contain  the  material,  allowing 
it  to  absorb  heat  before  it  reaches  the  melting  zone. 

Before  starting  the  fire  for  each  day's  melt,  the  lining  of  the 
cupola  should  be  inspected  and  repaired.  The  bottom  doors 
are  then  closed,  and  tempered  sand  is  rammed  on  the  bottom, 
forming  a  floor  inclining  toward  the  tap-hole.  After  the  first 
charge  of  coke  is  ignited,  the  "  breast  "  is  built  around  the  tap- 
hole.  This  is  often  done  by  removing  the  coke  that  has  fallen 
into  the  breast  opening,  building  a  wall  of  the  cold  coke  back  of 
the  opening,  and  then  building  up  a  wall  of  fire-clay,  thru 


284  APPENDIX  B 

which  a  pin  is  inserted.  This  pin,  when  removed,  leaves  the 
tap-hole.  When  the  wall  of  coke  is  ignited,  the  breast  is  baked, 
and  the  furnace  is  ready  for  the  charge  of  iron  and  the  blast. 
The  blast  pressure  should  not  exceed  i  Ib.  per  sq.  in.  Coke  is 
most  commonly  used  as  fuel,  altho  anthracite  is  occasionally 
used. 

Ladles.  Ladles  vary  in  size  from  the  small  hand  ladles  car- 
ried by  one  man  to  the  large  bull  ladles  having  a  capacity  of 
many  tons.  Small  ladles  are  usually  lined  with  fire-clay  and  the 
larger  ones  with  fire-brick.  Large  ladles  must  be  provided  with 
a  mechanism  for  tilting  them  for  pouring.  All  ladles  should 
have  their  lining  heated  by  a  gas  flame  or  coke  fire  before  receiving 
the  molten  iron,  to  prevent  both  the  cracking  of  the  lining  and 
the  chilling  and  spattering  of  the  molten  iron. 

Rattling  or  Tumbling  Barrels.  These  should  be  of  different 
sizes  to  suit  different  kinds  of  work,  with  a  mechanism  for  rotat- 
ing. The  cleaning  is  done  by  the  impact  of  "  stars  "  or  "  picks  " 
with  which  the  barrel  is  filled.  Sometimes  there  is  used  an 
equipment  for  directing  a  blast  of  sand  against  the  castings  being 
tumbled. 

Pickling  Vats.  It  is  sometimes  necessary  to  pickle  castings 
in  dilute  sulfuric,  hydrochloric  or  hydrofluoric  acid  in  order  to 
remove  green-sand  scale.  Vats  and  troughs  of  wood  or  stone 
filled  with  acid  are  then  used.  Castings  so  treated  should  always 
be  well  rinsed  in  clean  water. 

Cleaning  Tools.  Small  tools  operated  by  hand  or  compressed 
air  are  necessary  for  cleaning  the  scale  from  the  outside  of  cast- 
ings and  for  breaking  out  the  core  sand  from  the  interiors. 

Common  Defects  of  Iron  Castings.  The  most  common 
faults  of  iron  castings  are  blowholes,  sponginess,  shrink-holes, 
scabbiness,  sand-holes,  floating  cores,  cold  shuts,  cold  shot, 
strains,  shrinkage  strains  and  warp.  These  may  occur  even 
though  the  mold  is  in  good  condition. 

i.  Blowholes  are  probably  the  most  common  defect.  These 
are  holes  in  the  castings  caused  by  imprisoned  gases.  They  are 
often  invisible  on  surface  inspection  and  are  most  apt  to  occur 


FOUNDRY  PRACTICE  285 

near  the  top  of  a  casting.  Other  conditions  permitting,  those 
parts  of  the  casting  which  are  to  be  machined  or  which  require 
the  most  strength,  should,  therefore,  be  at  the  bottom  of  the 
mold  when  it  is  poured.  The  gases  which  form  blowholes  con- 
sist of: 

a.  Steam  generated  from  moisture  in  the  sand. 

b.  Gases  arising  from  decomposition  of  the  facing  material. 

c.  Air  entrapped  in  various  cavities  of  the  mold. 

The  remedy  for  all  these  is  to  provide  a  means  for  the  escape  of 
gases  by  venting  and  by  risers.  Since  vent  holes  cannot  extend 
to  every  point  near  the  surface  of  the  molds,  the  gases  must  pass 
thru  the  sand  until  they  reach  the  nearest  vent  hole.  There- 
fore, the  sand  must  have  porosity,  which  it  cannot  have  if  too 
tightly  rammed  or  too  wet,  or  if  the  grains  are  not  of  the  correct 
size  and  shape  for  the  work  in  hand. 

2.  Sponginess  is  caused  by  the  formation  of  gas  bubbles  in 
the  iron  at  the  instant  of  solidification.     It  is  due  to  an  improper 
mixture  of  iron  charged  to  the  cupola.     If  a  casting  is  thick  at 
one  place  and  thin  at  another,  sponginess  can  be  prevented  by 
providing  a  riser  or  shrink-head  at  the  thick  part.     To  avoid 
sponginess  where  it  is  not  possible  to  place  a  riser,  let  no  part  of 
the  iron  be  more  than  3  in.  from  a  sand  surface. 

3.  Shrink-holes  are  caused  by  the  shrinking  of  the  metal  in 
cooling.     It   occurs   where   a   casting  is   extra   thick.     Shrink- 
holes  are  prevented  by  avoiding  sudden  changes  in  the  thickness 
of  a  section,  by  the  use  of  a  shrink-head,  or  by  chilling  the  thick 
portions.     The   designer   should   avoid   heavy   sections   where 
possible,  but  where  such  are  necessary,  they  should  be  so  ar- 
ranged as  to  permit  the  use  of  a  riser  directly  over  them. 

4.  Scabbiness  is  caused  by  loosening  the  surface  sand,  or 
erosion  of  the  fillers  and  partitions  by  the  force  of  the  inflowing 
iron.     The  remedy  is  to  avoid  sharp  edges  on  fillets  and  tongues 
of  sand,  and  to  gate  the  mold  so  that  the  current  of  entering  iron 
will  be  evenly  spread. 

5.  Sand-holes    are    associated    with    scabbiness.     They    are 
caused  by  the  same  conditions,    except  that  in  their  formation 


286  APPENDIX  B 

the  iron  has  solidified  at  the  .surf  ace,  thus  preventing  the  loosened 
sand  from  floating  entirely  to  the  top.  This  leaves  it  imprisoned 
in  the  body  of  the  casting. 

6.  Floating  Cores  are  caused  by  a  core  of  insufficient  strength 
to  resist  the  buoyant  effect  of  the  molten  iron. 

7.  Cold  Shuts  are  caused  by  the  imperfect  union  of  two  or 
more  streams  of  molten  iron  in  the  mold,  too  cold  to  coalesce  on 
meeting.    They  occur  when  the  iron  must  flow  some  distance 
thru  a  thin  part  of  the  mold.      The  remedy  is  to  use  iron  as 
hot  and  fluid  as  possible,  and  to  arrange  gates  so  that  the  iron 
will  quickly  fill  up  the  mold. 

8.  Cold  Shot  are  small  globules  of  iron,  imperfectly  united 
with  the  rest  of  the  casting,  and  hard  or  impossible  to  machine. 
They  are  caused  by  the  splashing  of  the  iron  in  pouring,  the 
spattered  drops  becoming  chilled  and  dropping  to  the  bottom  of 
the  mold.     Splashing  is  usually  caused  by  a  gate  dropping  iron 
directly  into  a  web,  or  by  pouring  so  slowly  as  to  allow  the  iron 
to  "  dribble  in."    The  remedy  is  obvious. 

9.  Strains.    This  term  covers  a  casting  with  warped  walls 
due  to  the    outward  yielding  of    the  sand  walls  of  the  mold. 
This  is  caused  by  loose  ramming  and  insufficient  weights. 

10.  Shrinkage  or  Internal  Strains  are  caused  by  unequal  rates 
of  cooling.     To  avoid  them,  arrange  the  thickness  of  the  parts  so 
that  the  entire  casting  will  solidify  at  about  the  same  time,  or 
else  chill  the  thick  portions. 

11.  Warping  is  caused  by  shrinkage  strains  that  are  suf- 
ficient to  alter  the  shape  of  the  finished  casting.     It  is  due  either 
to  a  want  of  symmetry  in  the  design  of  sectional  parts,  and  the 
consequent  unequal  contraction  in  cooling,  or  to  dumping  out  the 
casting  from  the  sand  while  still  hot  and  soft,  allowing  them  to 
become  chilled  on  one  side  by  air  currents,  or  to  sag  of  their  own 
weight. 

Reference  on  Foundry  Work.  "  Elementary  Foundry  Prac- 
tice," Richards;  "  Foundry  Practice,"  Tate  and  Stone; 
"  Foundry  Practice,"  Palmer;  "  Metallurgy  of  Iron  and  Steel," 
Bradley  Stoughton. 


GLOSSARY   OF   TERMS    IN   COMMON    USE 

ARBOR.    A  bar  or  mandrel  used  as  the  center  on  which  is  built  a  core. 

ANNEAL.    To  soften  or  render  ductile  by  the  application  of  heat  either 
with  or  without  a  carbonaceous  material  packed  around  it. 

BAKED  CORE.    A  dry-sand  core  which  has  been  subjected  to  heat 
(usually  in  an  oven)  to  render  it  hard  and  to  fix  its  shape. 

BASIN.    The  portion  of  a  cupola  in  which  the  molten  iron  collects. 

BED  CHARGE.    The  first  coke  charged  into  the  cupola. 

BENCH  WORK.    Molds  of  such  size  that  they  can  be  made  at  the  bench. 

BINDER.    A  bar  of  wood  or  iron  with  slotted  ends  to  receive  bolts, 
placed  across  a  cope  to  hold  the  cope  to  the  drag. 

BLAST.    The  supply  of  air  to  the  cupola. 

BOD.  A  ball  of  clay  for  closing  the  tap-hole. 

BOSH.    Same  as  a  swab.    See  page  290. 

BOTTOM  BOARD.    A  board  placed  under  a  mold. 

BLOWHOLE.    A  defect  in  a  casting  caused  by  gases  which  do  not  escape. 

BREAK-OUT.    A  rupture  of  a  mold  permitting  metal  to  flow  out  at  the 
joint.    Also  called  a  "  run-out." 

BREAST.    The  portion  of  the  lining  of  a  cupola  immediately  surrounding 
the  tap-hole. 

BUCKLES.    Swellings  in  the  surface  of  a  mold  due  to  the  generation  of 
steam  below  the  surface  which  cannot  escape. 

CARRYING  PLATES.    Iron  plates  used  to  support  certain  parts  of  molds. 

CHAPLET.    A  piece  of  metal,  shaped  in  various  ways,  placed  in  a  mold 
to  support  a  core. 

CHARGE.    The  iron  and  fuel  placed  in  the  cupola  or  air-furnace. 

CHEEK.    That  portion  of  a  three-part  mold  between  the  core  and  the 
drag. 

CHILL.    An  iron  surface  of  a  mold,  sometimes  water-cooled,  used  to  chill 
the  molten  iron  rapidly  and  thus  produce  a  hard  surface. 

CHURNING.    See  Pumping. 

CLAMPING  BAR.    A  bar  used  to  tighten  clamps  on  a  flask. 

CLAMPS.    Devices  for  fastening  copes  and  drags  together. 

COLD  SHUT.     An  imperfection  in  the  casting  due  to  the  metal  entering 
the  mold  by  different  sprues,  cooling,  and  failing  to  unite. 

COPE.    The  upper  half  of  a  mold. 

287 


288  APPENDIX  B 

COPE  DOWN.  To  build  projecting  bodies  of  sand  on  the  surface  of  the 
cope  to  form  surfaces  on  the  casting  which  are  below  the  level  of  the  joint 
of  the  drag. 

CORE.  A  body  of  sand,  either  green  or  dry,  placed  in  a  mold  to  form  a 
cavity  in  the  casting. 

CORE  Box.    A  box  in  which  cores  are  formed. 

CORE-PLATE.     A  flat  iron  on  which  green  cores  are  placed  for  baking. 

CORE  PRINT.  The  cavity  in  a  mold  in  which  the  ends  of  the  cores  are 
set.  The  projections  on  a  pattern  which  form  and  locate  the  prints  in  the 
mold. 

DRAFT.  The  taper  given  in  the  sides  of  a  pattern  which  enable  it  to  be 
easily  withdrawn  from  the  molds. 

DRAG.    The  lower  section  of  the  mold. 

FALSE  CHEEK.  A  body  of  sand  in  a  mold,  occupying  the  same  position 
and  performing  the  same  function  as  a  cheek,  but  contained  within  the 
cope  and  drag,  altho  separate  from  them. 

FLASK.  The  framework  of  wood  or  iron  in  which  the  sand  is  packed 
while  being  molded  around  the  pattern. 

FLAT-BACK.  A  pattern  with  a  flat  surface  at  the  joint  of  the  mold. 
Thus  a  flat-back  pattern  lies  wholly  within  the  drag,  and  the  joint  of  the 
cope  is  a  plane  surface. 

FLOW-OFF.  A  channel  cut  from  a  riser  to  permit  metal  to  flow  away  from 
it  when  it  has  risen  to  a  certain  height. 

GAGGERS.  Rods  of  wrought  or  cast  iron  with  one  end  bent  at  a  right 
angle  used  to  support  hanging  bodies  of  sand  in  a  mold. 

GATE.    The  hole  in  the  cope  thru  which  metal  is  poured  into  a  mold. 

GREEN  CORE.    A  core  which  has  not  been  baked. 

GREEN  SAND.  Ordinary  molding  sand  which  has  not  been  baked  or 
given  other  heat  treatment  except  by  contact  with  molten  metal  in  a  mold. 

GREEN-SAND  MATCH.  A  false  cope  in  which  patterns  are  placed  while 
a  drag  is  being  made.  Its  object  is  to  avoid  making  a  difficult  joint  in  each 
mold  where  a  number  of  castings  are  to  be  made  from  the  same  pattern. 

JOINT.    That  portion  of  a  mold  where  the  cope  and  drag  come  together. 

LOAM.     A  mixture  of  molding  sand  and  clay  for  making  loam  molds. 

MELTING  ZONE.  That  part  of  the  cupola  above  the  tuyeres  zone  where 
the  metal  fuses. 

MOLD  BOARD.  The  board  on  which  patterns  are  laid  when  making  a 
drag. 

NOWEL.     A  large  core,  usually  in  a  loam  mold. 

PARTING.    The  place  on  which  the  pattern  is  split. 

PEG  GATE.  A  round  gate  leading  from  a  pouring  basin  in  the  cope  to  a 
basin  in  the  drag,  whence  sprues  lead  into  the  mold. 


GLOSSARY  OF  TERMS  IN   COMMON  USE  289 

POURING  BASIN.    A  basin  formed  in  the  cope  into  which  iron  is  poured. 

PUMPING.  The  action  of  feeding  iron  to  a  casting  from  a  shrink-head 
by  forcing  it  in  with  a  rod  moved  up  and  down  in  the  shrink-head. 

RISER.  A  gate  formed  over  a  high  portion  of  a  mold  to  act  as  an  indi- 
cator when  the  mold  is  filled  with  metal  and  also  to  act  as  a  feeder  to  supply 
iron  to  the  casting  as  it  shrinks. 

RUNNER.  A  deep  channel  formed  in  the  top  of  the  cope  connecting  with 
gates  into  which  the  iron  is  poured. 

SCABS.  Imperfections  in  a  casting  due  to  the  surface  of  the  mold  having 
broken  and  allowed  the  loose  sand  to  become  imbedded  in  the  iron. 

SHRINK-HEAD.  A  large  riser  containing  a  sufficient  body  of  metal  to 
act  as  a  feeder  for  metal  contracting  upon  solidification. 

SHOT.  Globules  of  metal  formed  in  the  body  of  a  casting  and  harder 
than  the  remainder. 

SKIM  GATE.  A  sprue  so  arranged  as  to  skim  any  impurities  from  the 
surface  of  the  molten  iron  as  it  flows  into  the  mold. 

SKIN-DRIED  MOLD.  A  green  sand-mold  whose  surface  has  been  baked 
for  a  depth  of  an  inch  or  more. 

SNAP  FLASK.  A  flask  hinged  at  the  corners,  and  separable  at  one  corner 
so  as  to  allow  its  removal  from  a  complete  mold. 

SOLDIER.  A  wooden  stick  or  rod,  clay-washed,  used  to  support  bodies 
of  hanging  sand  or  large  green-sand  cores. 

SPRUE.  The  channel  leading  from  the  gate  to  the  mold.  The  metal 
which  solidifies  in  this  channel  and  adheres  to  the  casting  after  cooling. 

SWEEP.  A  piece  of  wood  or  iron  revolved  about  a  center  to  form  the 
surface  of  a  mold. 

TIGHT  FLASK.    A  flask  with  a  rigid  frame;  the  opposite  of  "  snap  flask." 

TUYERES.    The  openings  in  a  cupola  thru  which  air  is  blown. 

UPSET.  A  shallow  frame  set  over  a  flask  in  which  a  green-sand  match 
is  formed. 

VENT.  A  small  hole  formed  in  a  mold  to  permit  escape  of  gas 
from  it. 

WHIRL  GATE.  A  gate  or  sprue  arranged  to  introduce  metal  into  a  mold 
tangentially,  and  to  thereby  give  a  swirling  motion. 

COMMON  TOOLS  USED  BY  THE  MOLDER 

Shovel  used  for  cutting  up  a  sand  heap  and  filling  a  flask. 

Water  pail  used  for  wetting  down  the  sand  for  tempering,  and  for  wet- 
ting a  swab,  or  a  bosh  on  floor  molding. 

Riddle,  a  sieve  used  for  sifting  sand  on  the  surface  of  a  pattern  when 
starting  a  mold.  The  size  of  riddle  is  designated  by  the  number  of  meshes 


290  APPENDIX  B 

per  linear  inch.  Fine  castings  with  surface  detail  require  finer  sand,  hence 
a  finer  riddle. 

Rammers  used  for  pounding  sand  around  the  patterns  in  the  flask. 
Small  rammers  are  of  maple,  larger  ones  of  iron. 

Strike,  used  for  scrape  off  extra  sand  not  wanted  from  the  top  surface  of  a 
cope  or  drag.  A  board  or  thin  strip  of  bar  iron. 

Gaggers  and  soldiers  for  holding  sand  pockets.     See  page  289. 

Bellows  used  to  blow  parting  sand  from  the  pattern,  also  to  blow  loose 
sand  and  dirt  from  surface  of  mold. 

Bosh  or  swab.  A  bundle  of  hemp,  pointed  at  one  end;  bound  with  twine 
at  the  other.  Used  to  squeeze  water  around  the  edge  of  the  pattern  before 
drawing.  Used  also  the  apply  wet  blacking  to  dry-sand  molds  before  drying. 

Rapping  and  clamping  bar  of  steel;  pointed  at  one  end  to  enter  rapping 
plates  in  patterns;  flattened  and  turned  up  at  the  other. 

Rapping  iron  used  to  strike  a  rapping  bar  entering  thru  a  gate  hole 
in  order  to  jar  all  faces  of  the  pattern  at  same  time. 

Draw-screws  or  eye-bolts  threaded  on  one  end.  Used  to  draw  large  wood 
or  metal  patterns  from  a  mold. 

Draw-spike,  steel,  pointed  at  one  end.  For  rapping  and  drawing  pat- 
terns. Used  mostly  on  bench  work  for  small  patterns. 

Spring  Draw  Nail.  Used  for  drawing  small  patterns.  Two  rods 
joined  by  spring,  press  outward  and  grip  the  pattern  when  released. 

Wooden  Gate  Pin,  or  Sprue.  A  round  tapered  pin  used  to  form  a  gate 
thru  the  cope  into  which  iron  is  poured. 

Gate-  or  Sprue-Cutter.  A  sheet  of  brass,  semi-circular  at  the  edge,  used 
to  cut  a  channel  in  the  drag  from  the  gate  to  the  mold. 

Vent  Wires.  Steel  wires,  upset  on  one  end,  and  with  a  handle  on  the 
other,  used  to  "  vent  "  or  to  make  perforations  for  the  escape  of  gases  from 
the  mold. 

Clamps,  used  in  many  styles  and  sizes  in  conjunction  with  wedges,  for 
holding  the  cope  and  drag  tightly  together. 

MOLDER'S  SMALL  TOOLS 

(The  following  are  tools  usually  furnished  and  owned  by  the  molder 
himself.) 

Trowels  of  different  styles  and  sizes,  used  for  making  the  joint  on  a 
mold,  and  for  finishing  and  smoothing  surfaces. 

Slickers,  used  for  smoothing  or  slicking,  patching,  building  up  sand, 
forming  corners,  etc.  Different  styles  are  known  as  "  bead "  slickers, 
"  spoon  "  slickers,  "  double-enders,"  etc.,  and  are  used  on  different  kinds 
of  curved  and  straight  surfaces. 


GLOSSARY  OF  TERMS  IN  COMMON  USE  291 

Corner  Tools,  for  slicking  corners,  both  inside  and  outside. 

Pipe  tools,  usually  of  cast  iron,  with  a  handle  set  vertically  in  the  center. 
Used  for  slicking  interior  of  cylindrical  surfaces. 

Flange  tools,  of  steel.    Used  for  slicking  flanges  on  pipes  or  cylinders. 

Hub  tools,  used  in  cylindrical  portions  of  molds  such  as  hubs  of  pul- 
leys which  are  too  small  to  permit  the  use  of  a  pipe  slicker. 

Lifters,  used  in  lifting  loose  sand  from  deep  places  in  the  mold.  The 
heel  of  the  lifter  is  also  used  to  slick  the  deep  places  after  the  loose  sand  has 
been  removed. 


APPENDIX  C 


GENERAL  DIRECTIONS  FOR  WRITTEN  WORK  * 
MECHANICAL  DETAILS 

Paper.  Standard  ruled  note-book  paper  or  a  prescribed 
equivalent  must  be  used.  For  typewritten  work,  title  pages, 
and  sketches,  blank  paper  is  required.  Tabulated  data  and 
curves  should  be  put  on  the  special  forms  of  paper  designated 
for  these  parts  of  the  report. 

Ink.  All  exercises  should  be  written  in  dark  ink.  Pencil 
sketches  are  sometimes  permissible  in  inspection-trip  and 
laboratory  reports,  but,  unless  otherwise  specified,  drawings 
should  be  inked  in  with  India  ink. 

Page  Numbering.  All  pages  should  be  numbered  in  the 
upper  right-hand  corner.  It  is  well  to  indicate  also  the  experi- 
ment or  series  of  experiments  to  which  a  particular  page  refers. 

Paragraph  Indentation.  Paragraphs  should  be  indented  at 
least  i  in. 

Margins.  The  left-hand  margin  should  be  kept  straight, 
and  flush  with  the  red  line.  The  right-hand  margin  may  be 
slightly  irregular,  but  should  not  be  crowded. 

Headings.  Sectional  headings  should  be  placed  in  the 
middle  of  the  page  and  should  be  separated  by  at  least  two 
spaces  from  the  divisions  between  which  they  occur.  Sub- 
headings should  appear  at  the  left,  as  in  the  foregoing  instruction 
sheets,  and  preferably  one  space  above. 

Formulas    and    Chemical    Equations.     Equations    and    for- 

*  By  C.  W.  Park,  A.M.,  Associate  Professor  of  English,  University  of  Cincinnati. 

292 


GENERAL  DIRECTIONS  FOR  WRITTEN  WORK        293 

mulas  should  be  dropped  to  the  middle  of  the  line  below  the  one 
in  which  they  are  introduced,  thus: 


or,  in  the  case  of  a  chemical  equation, 

Ca(HCO3)2  +  CaO  =  2CaC03  +H20. 

Chemical  Symbols.  In  connected  discourse,  the  name  of  a 
chemical  compound  and  not  its  formula  should  be  used.  If  the 
formula  is  given,  it  should  be  placed  in  parentheses  immediately 
after  the  name  of  the  compound,  thus: 

"  The  carbon  dioxide  (CCfe)  escapes,  and  the  calcium  car- 
bonate (CaCOs)  is  precipitated."  It  should  not  be  written, 

"  C02  escapes,  CaCOs  precipitated,"  unless,  perhaps,  in 
notes.  In  equations  and  in  tabular  statements,  of  course,  the 
symbols  should  regularly  be  used. 

Abbreviations.  Only  authorized  abbreviations,  such  as 
B.t.u.,  etc.,  should  be  used.  If,  for  example,  the  statement  just 
made  were  written, 

"  Only  auth.  abs.  should  be  used,"  the  confusion  arising 
from  the  use  of  the  unfamiliar  and  illegitimate  abbreviations 
would  more  than  offset  the  saving  in  space.  A  false  notion 
of  economy  of  expression  often  leads  writers  to  invent  for  their 
own  use  a  sort  of  cryptic  shorthand  which  is  neither  English 
nor  any  other  intelligible  language.  It  is  much  safer  to  write 
out  all  words  for  which  there  is  not  a  recognized  abbreviation. 
A  few  of  the  more  common  abbreviations  used  in  technical 
writing  are  given  below.  For  additions  to  this  list  and  for 
explanation  of  unfamiliar  abbreviations  which  he  encounters  in 
his  reading,  the  student  sliould  consult  one  of  the  larger  dic- 
tionaries. 

ans  .....................  answer 

B.t.u  ...................  British  thermal  units 

B.w.g  ...................  Birmingham  wire  gage 

C  ......................  centigrade 


294  APPENDIX  C 

cc cubic  centimeter 

cf compare  (Lat.  confer) 

cp candlepower 

cm centimeter 

cu cubic 

c.p chemically  pure 

deg.  (or  °) degree 

e.g for  example  (Lat.  exempli  gratia) 

e.m.f electromotive  force 

Fig Figure 

F Fahrenheit 

f.o.b free  on  board 

ft.  (or  0 feet 

gal gallons 

gm. gram 

gr grains 

H.P horsepower 

H.P.  hr horsepower  hour 

i.e that  is 

i.h.p indicated  horsepower 

in.  (or  ") inches 

inst the  present  month 

kv kilovolt 

km kilometers 

Ib pounds 

min minutes 

mm millimeters 

ms manuscript 

no number 

oz ounce 

r.p.m rotations  per  minute 

sec seconds 

sp.gr specific  gravity 

sq.f t square  feet 

t tons 

ult the  preceding  month 


GENERAL  DIRECTIONS  FOR  WRITTEN  WORK       295 

viz namely 

vol volume 

vs against 

yd yard 

Figures.  Use  figures  for  dimensions,  distances,  measures, 
weights,  degrees  (of  angles  or  temperature),  dates,  specific 
gravity  and  decimals.  Examples  are  as  follows:  4  by  6  ft.; 
100  yd.;  12  gal;  13  oz.;  212°;  Jan.  5;  0.005. 

Exception:  Figures  should  not  be  placed  at  the  beginning  of 
a  sentence. 

Spell  out  isolated  enumerations  of  one  or  two  words;   e.g., 
"  four  propellers,"  "  twenty-five  separate  parts." 

In  a  compound  adjective,  one  element  of  which  is  a  numeral, 
the  figures,  rather  than  the  word  should  be  used;  e.g.,  28-inch 
mains,  a  1 6-pound  sledge. 

Sketches  and  Other  Illustrations.  Wherever  possible,  a 
sketch  or  a  photograph  should  be  used  to  illustrate  the  more 
difficult  and  the  more  important  parts  of  a  report.  These  illus- 
trations should  be  placed  within  the  text,  or  in  the  case  of  full- 
page  sketches  and  photographs,  immediately  after  that  part  of 
the  text  in  which  they  are  described.  Each  figure  should  be 
given  a  title  that  will  explain  its  connection  with  the  read- 
ing matter,  and  should  be  designated  as  "  Fig.  2,"  etc.,  in 
order  that  reference  may  be  made  to  it  in  other  parts  of  the 
report. 

Curves.  In  plotting  curves,  choose  the  scale  of  abscissae  so 
that  the  largest  value  reaches  nearly  or  quite  across  the  page. 
Choose  the  scale  of  ordinates  in  a  similar  manner.  Always 
select  the  units  so  that  each  graduation  of  the  cross-section 
paper  represents  a  convenient  number  of  units  or  a  convenient 
fractional  part  of  a  unit.  The  two  scales  need  not  be  alike, 
but,  in  general,  similar  quantities  should  have  similar  scales. 

The  independent  variables  are  usually  plotted  as  the  abscissae 
and  the  dependent  variables  as  the  ordinates.  An  exception  to 
this  rule  is  found  in  the  case  of  load-deformation  curves.  Defor- 


296  APPENDIX  C 

mations  (deflections,  elongations)  are  invariably  plotted  as 
abscissae  and  the  loads  as  ordinates. 

When  the  graph  is  a  calibration  curve,  and  it  is  certain  that 
there  is  no  error  of  observation,  the  curve  should  be  a  smooth 
line  passing  thru  every  point.  In  case  of  other  curves,  always 
draw  the  straight  line  or  the  smooth  curve  that  most  nearly 
fits  all  of  the  points  plotted.  Deviations  from  the  points  in 
the  curve  usually  indicate  errors  of  observation.  Such  errors 
are  corrected  by  drawing  the  curve  thru  the  mean  position 
of  the  points. 

Give  each  curve  a  title;  e.g.,  "  Cooling  Curve  of  Pure  Iron." 
The  curve  sheet  should  also  contain  the  name  of  the  observer, 
the  names  of  his  assistants,  the  source  of  the  data,  and  a  desig- 
nation of  the  apparatus  or  material  to  which  the  curve  applies. 
The  data  and  information  given  on  the  curves  should  be  sufficient 
for  the  application  or  interpretation  of  the  curves  without 
reference  to  any  other  part  of  the  report. 

Black  drawing  ink,  French  curves,  and  a  ruling  pen  must  be 
used  in  drawing  curves.  The  curve  should  ordinarily  be  a  full 
line,  but  in  case  two  or  more  curves  are  drawn  close  together 
some  distinction  should  be  made  in  order  to  avoid  confusion. 
Such  distinctions  may  be  made  clear  by  broken  lines,  different 
colored  inks,  and  different  geometrical  figures  (circles,  triangles, 
etc.),  to  indicate  the  points  of  the  curve.  Broken  lines  may 
also  be  used  to  indicate  hypothetical  extensions  of  known 
curves. 

Details  for  Identification  of  Manuals.  Each  laboratory 
manual  should  contain  the  following  data: 

Name  of  student. 
Course. 
Squad  number. 

Condition  of  Manuscript.  No  manuscripts  should  be  sub- 
mitted which  contain  blots,  insertions,  or  crossed-out  passages. 
Erasures,  if  any  are  necessary,  should  be  neat  and  inconspicuous. 
All  work  should  be  carefully  revised  and  carefully  prepared  in  a 


THE  WRITING  OF  REPORTS  AND  ABSTRACTS        297 

neat  and  legible  form  before  it  is  submitted  to  the  instructor. 
The  sheets  should  be  inserted  in  their  proper  sequence,  and 
should  be  bound  securely  in  the  laboratory  book. 

THE  WRITING  OF  REPORTS  AND  ABSTRACTS 

Typical  Outline  for  a  Laboratory  Report.  Altho  labora- 
tory reports  differ  widely  in  subject  matter,  the  problem  of 
organization  is  very  similar  in  all  of  them.  The  outline  given 
below  represents  a  logical  development  of  the  subject  as  well  as  a 
convenient  distiibution  of  the  material  in  the  report  of  a  test. 
With  a  few  changes  here  and  there  to  fit  special  conditions, 
this  form  will  be  found  serviceable  in  the  writing  of  nearly  every 
kind  of  laboratory  report. 

(1)  Object.     This  division  should  consist  of  a  clear,  full,  and 
concise  statement  of  the  object,  preferably  in  the  form  of  a 
simple  declarative  sentence.     Since  the  report  is  not  written 
until  after  the  test  has  been  performed,  the  statement  should 
be  put  in  the  past  tense;  e.g.: 

"  The  object  of  this  test  was  to  determine  the  steam  consump- 
tion of  a  Brownell  10X12  engine." 

(2)  Theory.     This  division  should  contain  a  general  state- 
ment of  that  data  to  be  obtained  in  such  a  test,  together  with  the 
fundamental  principles  on  which  the  test  depends.     For  example, 
the  second  paragraph  of  the  report  indicated  above  might  begin 
as  follows: 

"  In  testing  for  steam  consumption,  the  chief  data  to  be 
obtained  are  (a)  the  horsepower  of  the  engine,  and  (b)  the  weight 
of  the  steam  passing  thru  the  cylinder  in  a  given  time." 

Where  formulas  are  to  be  applied  in  the  test,  they  should 
be  given  in  this  part  of  the  report. 

Since  the  discussion  deals  with  general  theory,  this  section 
of  the  report  should  be  expressed  in  the  present  tense. 

(3)  Apparatus.    The  apparatus  used  should  be  described, 
with  emphasis  on  new  apparatus  and  on  special  devices  used  in 
the  particular  test  in  question.     At  the  beginning  of  the  section 


298  APPENDIX  C 

the  various  pieces  of  apparatus  should  be  enumerated.  New 
and  special  pieces  may  then  be  described  in  detail. 

In  so  far  as  this  part  of  the  report  deals  with  particular  appa- 
ratus, it  should  be  put  in  the  past  tense,  e.g. : 

"  The  apparatus  used  in  this  test  consisted  of  the  follow- 
ing:" etc. 

(4)  Procedure.     This  section  contains  an  account  of  what 
was  done  in  carrying  out  the  successive  parts  of  the  test.     Care 
should  be  taken  to  omit  preliminary  and  non-essential  opera- 
tions, and  to  follow  the  actual  order  in  which  the  work  was  done. 

The  narrative  should  be  impersonal,  and  should  be  given  in 
the  past  tense  and  the  passive  voice;  e.g.: 

"  Readings  were  taken  at  intervals  of  five  minutes,"  etc. 

(5)  Results,     a.  Summary   of   results.     Conclusions   drawn 
from  the  data  should  be  stated  briefly  and  clearly.     In  some 
cases  it  may  be  desirable  to  compare  them  with  results  obtained 
in  other  tests. 

b.  Curves  (seepage  295). 

c.  Sample  calculations.     They  may  be  brief,  but  they  should 
be  typical  of  the  mathematical  processes  involved  (see  page  230). 

d.  Data. 

The  data  should  be  presented  on  special  ruled  paper 
designed  for  the  purpose.  It  should  be  arranged  in  tabular 
form  and  in  parallel  columns. 

(6)  Sketches  (seepage  295). 

(7)  Original   Data.     Rough   notes    taken    during    the    test 
should  be  submitted  from  time  to  time  as  evidence  of  the  accuracy 
with  which  observations  were  made.     If  a  log  book  is  kept,  it 
will  answer  the  purpose. 

The  Writing  of  Abstracts.  An  abstract  summarizes  briefly 
in  connected  discourse  the  gist  of  a  discussion.  Unlike  the 
synopsis,  which  may  be  more  or  less  fragmentary  or  discon- 
nected, the  abstract  is  a  complete  composition,  a  miniature 
reproduction  of  a  larger  work.  Comment,  an  important  feature 
of  the  review,  is  lacking  in  the  abstract,  and  the  latter  form  con- 
tains little  or  no  quoted  matter.  The  abstractor,  using  his  own 


THE  WRITING  OF  REPORTS  AND  ABSTRACTS        299 

language  and  keeping  the  proportions  of  the  original,  restates 
compactly  the  main  points  in  the  discussion.  The  making  of  an 
abstract  is  thus  a  test  of  his  ability  both  to  digest  another's 
work  and  to  write  clearly  and  smoothly. 

For  purposes  of  illustration,  the  foregoing  paragraph  may  be 
regarded  as  an  abstract  of  a  short  lecture  on  the  writing  of 
abstracts.  Roughly  speaking,  each  sentence  in  the  summary 
is  a  condensed  statement  of  the  thought  in  a  paragraph  or  a 
section  of  the  lecture.  The  relation  between  the  divisions  of  the 
longer  discussion  should  therefore  be  reflected  in  the  connection 
between  the  sentences  in  the  summary  paragraph.  Another 
illustration  is  an  abstract  of  the  matter  contained  on  p.  313 
of  "  Materials  of  Construction,"  by  A.  P.  Mills: 

Paragraph  351.     "  Pouring  the  Iron  " 

"  The  molten  iron  is  transferred  from  the  cupola  to  the  molds  in  heated 
clay-lined  ladles  of  the  top-pouring  type.  Small  molds  are  filled  from  hand 
ladles;  for  larger  castings  ladles  of  sufficient  capacity  are  carried  on  trucks  or 
by  cranes.  A  gentle,  steady  and  uniform  stream  of  quiet,  slag-free  metal 
sufficient  to  fill  the  entire  cavity  should  be  gently  poured  into  the  mold,  which 
is  ordinarily  broken  up  soon  after  the  solidification  of  the  iron,  to  allow  the 
casting  to  cool  more  rapidly." 

Place  at  the  beginning  of  each  abstract  a  complete  reference 
to  the  original  article.  The  method  of  noting  the  volume 
numbers  by  a  numeral  preceding  the  name  of  the  publication, 
and  the  page  numbers  by  numerals  immediately  following  the 
name  of  the  publication  is  universally  used  in  legal  publica- 
tions, is  compact  and  clear  and  much  to  be  recommended. 
Wherever  possible  page  numbers  should  be  inserted  to  indicate 
the  length  of  the  article.  For  instance, 

Aitchison,  Leslie.  "  The  Theory  of  the  Corrosion  of  Steel."  15  Metal- 
lurgical and  Chemical  Engineering,  88-92. 

The  following  example  is  quoted  from  20  (I)  Science 
Abstracts,  15. 

"  Apparatus  for  the  Commercial  Testing  of  Permanent  Magnets.  B.  G. 
Betteridge.  (98  Electrician,  213-215,  Nov.  17,  1916.)  The  manufacture 


300  APPENDIX  C 

of  large  numbers  of  steel  magnets,  for  magnetos  and  meters,  in  this  country, 
to  take  the  place  of  those  formerly  supplied  in  Germany,  has  necessitated  the 
design  of  suitable  testing  apparatus  for  the  magnets.  The  two  most  important 
features  the  manufacturer  requires  to  know  are  (a)  the  coercive  force  and  (b) 
the  remnant  flux.  Owing  to  the  large  number  of  magnets  to  be  tested,  the 
apparatus  should  satisfy  the  following  conditions  :  (i)  Allow  of  individual 
testing  of  magnets.  (2)  The  test  should  take  the  minimum  time  to  carry  out. 

(3)  The  apparatus  employed  should  be  as  simple  and  robust  as  possible. 

(4)  The  indications  obtained  should,  wherever  possible,  be  direct-reading  and 
readily  interpreted,  so  that  the  apparatus  could  be  used  by  comparatively 
unskilled  persons.     (5)  The  results  obtained  should  be  as  accurate  as  possible, 
and  should  give  as  far  as  possible,  the  true  value  of  the  magnetic  properties 
of  the  magnet.    The  author's  method  is  to  use  an  electromagnet  to  energize 
the  steel  under  test.      A  disc  is  rotated  in  an  air-gap  in  the  magnetic  circuit 
and  the  voltage  generated  in  the  disc  measured  on  a  milli voltmeter.      By  this 
method  accurate  measurements  of  the  flux  in  the  magnet,  and  the  magnetizing 
force  applied  to  it,  can  be  obtained.    By  varying  the  exciting  current  the 
properties  of  the  magnet  can  be  investigated  and  its  hysteresis  loop  obtained. 
The  author's  final  design  consisted  of  two  solenoids  mounted  on  a  base  con- 
taining the  flux-measuring  device  proper.    The  two  legs  of  the  horseshoe 
magnet  under  test  are  inserted  in  the  two  solenoids  and  rest  on  a  pair  of  angles 
in  an  aluminum  base.    These  angles  are  separated  by  non-magnetic  distance 
pieces,  and  in  the  space  between  runs  a  soft-iron  disc  having  a  copper  ring 
attached  to  its  outer  edge.    The  disc  is  carried  on  a  spindle  made  of  a  copper 
alloy.    A  carbon  brush  is  run  on  this  spindle,  and  another  on  the  periphery 
of  the  disc.    The  positions  of  the  two  solenoids  are  adjustable,  so  that  various 
sizes  of  magnets  can  be  tested.    The  magnetizing  force  applied  in  the  test  is 
obtained  by  multiplying  the  magnetizing  current  in  milliamps.  by  a  suitable 
constant.    The  soft-iron  disc  is  driven  by  a  small  motor;   the  millivolts  gen- 
erated in  the  disc,  when  multiplied  by  a  constant,  give  the  flux  in  the  magnet 
under  test.    Line  drawings  and  illustrations  are  given  of  the  apparatus,  and 
the  author  states  that  a  smart  operator  can  test  a  batch  of  magnets  for  coer- 
cive force  and  remanence  at  a  rate  of  about  30  to  45  seconds  per  magnet,  and 
get  results  within  an  extreme  error  of  2  per  cent." 

As  an  aid  in  the  study  of  a  subject,  it  is  well  to  practice 
regularly  the  making  of  abstracts  from  lectures  and  articles. 
One  of  the  best  schemes  for  the  preservation  of  these  summaries 
in  a  readily  accessible  form  is  to  take  notes  on  thin  paper,  cut 
slightly  less  than  the  page-size  of  the  text  used,  and  to  paste 
the  sheets  into  the  text  book  at  appropriate  places.  Interleaving 
paper,  gummed  along  one  edge,  may  be  obtained  for  this  purpose. 


THE  WRITING  OF  REPORTS  AND  EXTRACTS         301 

Small  loose-leaf  sheets  in  a  note-book  may  be  used  for 
abstracts  not  pasted  in  the  text-book,  but  cards  are  better  for 
cultivating  the  filing  habit.  One  side  of  a  5  by  8-inch,  or  both 
of  a  3  by  5 -inch  card  will  ordinarily  suffice  for  one  article. 
Notes  thus  taken  should  be  filed  according  to  a  definite 
indexing  system. 


INDEX 


Abbreviations,  293 
Abstracts,  297 
Accidents,  2 
Acid,  definition,  27 

metallurgical,  6 

refractory,  27 

slag,  33 
Additions  to  melts,  method  of  adding, 

223 

Air,  analysis,  243 
Alpha  iron,  126 

crystallization,  154 

hardness,  154 

magnetism,  154 
Allotropic  modifications,  1 26 

theory  01  hardening,  154 
Alloy  steels,  hardening,  153 
Alloy  systems,  70 
Alloys,  constitution  of,  79 
Alumina,  melting-point,  25 
Aluminates,  thermochemistry,  235 
Amorphous  cement,  134 
Amphoteric  substances,  33 
Annealing,  137,  157,  287 

furnace,  19 

practice,  159 

Anthracite,  analysis,  243,  246 
Antimony,  etching,  83 

-lead  alloys,  70 

melting-point,  66 
Anvils,  heat  treatment,  164 
Apparatus,  care  of,  2 

personal,  2 

special,  3 

squad,  2 
Arbor,  287 
Arc  furnace,  104 

temperature,  258 

welder,  45 


Arrests,  57,  70,  125 
Ashes  from  coal,  247 
Assignments,  lessons,  3 

queries,  4 
Atmosphere,  in  a  furnace,  10 

pressure  of,  240 
Atomic  weights,  226 
Attendance,  i,  4,  5 
Austenite,  152,  168,  213 

constitution,  168 

etching,  168 

formation,  152 

hardness,  168 

in  cast  iron,  213 

photomicrograph,  153,  168 
Augite,  35 

Baked  core,  287 

Ball  races,  heat  treatment,  163 

Barium  carbonate,  as  cementing  agent, 

183 

Base,  27, 36 

Base  metal  thermo-coupies,  51 
Basic  refractory,  27 

slag,  33 

Basin,  271,  287 

Battering  tools,  heat  treatment,  165 
Battery,  primary,  42. 
Bed  charge,  287 
Bedding-in  molds,  275 
Bench  molds,  280,  287 
Benzophenone,  boiling-point,  66 
Beta  iron,  126 

hardness,  154 
Binders,  279,  287 
Bituminous  coal,  analysis,  246 
Black  body,  112 

experimental  attainment,  112 
Blast,  287 


303 


304 


INDEX 


Blast  furnace,  19 

charge,  266 

operation,  262,  266 
Blistered  negatives,  88 
Blister  steel,  181 
Blowholes,  284,  287 
Bod,  287 

Boiler  corrosion,  204 
Boiler  makers'   tools,  heat  treatment, 

164 

Boiler  plate,  photomicrograph,  173,  174 
Boiling-point  apparatus,  46 

table,  66 

Borates,  thermochemistry,  235 
Bosh,  287 
Bottom  board,  287 
Boyle,  law  of,  240 

Brass  working  tools,  heat  treatment,  163 
Breakage  deposit  tickets,  i 
Break  out,  287 
Breast,  283,  287 
Brinell  machine,  95 

directions  for  use,  99 

hardness  numeral  table,  100 

limitations,  96 

-meter,  97 

oil,  100 

British  thermal  unit,  234 
Brittleness,  Stead^,  135 
Broaches,  heat  treatment,  164 
Buckles,  287 

Bucking  board  cleaning,  29 
Burden  of  furnaces,  262 
Burned  steel,  135 

Bush  hammers,  heat  treatment,  163 
By-product  coke-oven  gas  analysis,  249 

Calcine,  analysis,  263 
Calibration  curves,  296 

of  optical  pyrometers,  112 

of  radiation  pyrometers,  112 

of  thermocouples,  63 
Calorific  intensity,  257 

carbonaceous-fuel  furnaces,  103 

electric  furnaces,  104 

oxy-hydrogen  flame,  257 
Calorimetry,  233,  251 


Calory,  233 
Candle  lamp,  83 
Captain's  duties,  i,  3,  4 
Carbon,  influence  on  hardening  steel, 
141 

-iron  equilibrium  diagram,  126,  131 

monoxide  as  cement,  182,  185 
Carbides,  thermochemistry,  235 
Carbonates,  thermochemistry,  235 
Carborundum,     dissociation     tempera- 
ture, 25 
Carburizing,  180 

mechanism  of,  181 
Care  of  equipment,  2,  3,  4 
Carrying  plates,  287 
Caron's  cement,  183 
Case  carburizing,  180 

mechanism  of,  181 

exfoliation,  189 
Castings,  cost  factors,  269 

defects,  284 

design,  270 
Cast  iron: 

composition,  213,  217,  218 

cooling  curves,  213 

gray,  215 

mottled,  216 

physical  properties,  216 

white,  215 

Cast  steel,  photomicrograph,  136 
Cement: 

blending  of  raw  materials,  259,  261 

constituents,  259,  262 

refractory,  54 
Cementation  or  case  carburizing,  180 

by  carbonaceous  materials,  184 

by  carbon  monoxide,  182,  185 

by  charcoal,  183 

by  cyanides,  184 

by  hydrocarbons,  187 

by  molten  baths,  184 

furnaces,  187 

index,  259 

types,  185-187 

variables,  192 
Cementite,  127,  213 

effect  on  strength  of  cast  iron,  217 


INDEX 


305 


Cementite  etching,  168,  173,  177 

-ferrite  equilibrium  diagram,  127,  131 

habit,  173 

hardness,  173 

instability  of,  215 

primary,  173 
Chaplets,  279,  287 

Charcoal  as  cementing  agent,  180-183 
Charge  of  furnace,  262,  287 
Cheek,  274,  287 
Chemical  equations,  225,  292 

symbols,  293 
Chill,  287 

Chisels,  heat  treatment,  164 
Chucks,  280 
Churning,  287 

Circular  shapes,  molding  of,  277 
Clamping  bar,  287,  290 
Clamps,  287,  290 
Coal,  heat  of  combustion,  247 
Coke  oven  gas,  analysis,  249 
Cold-end  corrections,  53 

pail,  54 
Cold  shot,  286 
Cold  shuts,  286,  287 
Cold- working  hardness,  153 
Color  of  hot  bodies,  116 
Combustion,  243 

air  required,  243 

total  heat  of,  247 
Concentration,  19 
Conduction  in  furnaces,  105 

in  quenching  baths,  147 
Cones,  pyrometric,  8 

Seger,  8 
Constitution  of  alloys,  79 

of  metals,  134 
Contact  electromotive  force,  41 

and  electrolysis,  197 
Convection  in  furnaces,  105 

in  quenching  baths,  147 
Converters,  20 
Cooling  curves,  56 

cast  iron,  213 

inverse  rate,  76 

lead,  58 

plotting,  68 


Cooling  curves,  salt  solutions,  71 

steel,  126,  129 

water,  58 

white  metal,  76 
Cope,  271,  287 
Coping  down,  275,  288 
Copper  leaching,  199 

melting-point,  66 

reduction,  22 
Core,  279,  288 

box,  288 

oven,  279 

plate,  288 

print,  279,  288 
Corrosion,  12,  194 

factors,  41,  201,  202 

mechanism,  200 

of  boilers,  204 

of  busy  iron,  203 

of  homogeneous  metal,  203 

of  hot-water  systems,  204 

of  wrought  iron,  203 

short  time  tests,  202 
Counterboring  forgings,  143 
Cracking  in  heat  treatment,  142 
Cranes,  282 

Crucibles,  care  of,  3,  60 
Crucible  steel,  162 
Crystalline  grains,  134 

failure,  135 

growth,  135 

Crystallization  of  steel,  133-135 
Crystalls,  etching,  169 
Cup  and  cone  steel,  heat  treatment  164 
Cupellation,  13,  1 6 
Cupola,  282 

breast,  283 

operation,  283 

shell,  283 

Curves,  standard  practice,  5,  295 
Cutlery,  164 
Cutting  hardness,  94 

molding  sand,  210 
Cyanide  as  cementing  agent,  184 

Decomposition,  heat  required.  238 
Defects  of  castings,  284 


306 


INDEX 


Deposit  tickets,  i 
Design  of  castings,  270 

electrical  furnaces,  104 
Developer,  88 
Development  of  negatives,  87,  92 

of  photographic  paper,  88,  92 
Die  castings,  270 
Dies,  heat  treatment,  163-165 
Diffusion    of    carbon    into   iron,    180, 
181 

of  CO  :  CO2  into  iron,  182,  185 
Diopside,  melting-point,  66 
Dirty  negatives,  88 

prints,  88 
Dissociation,  194 

Double  decomposition,   thermochemis- 
try of,  238 
Draft,  288 
Drag,    271,    288 
Draw  screws,  290 

spike,  290 

Drifts,  heat  treatment  of,  164 
Dry-sand  molds,  280 

Eckel's  rule,  261 
Electric  furnaces,  102 

advantages,  103 

design,  104 

temperature  attainable,  104 

tube,  1 06 

types,  104 

Electrolysis,  196,  197 
Elements,  see  thermo-couple  elements. 
Emissivity,  106 

hot  body,  116 

measurement,  123 

theoretical  black  body,  112 

variation,  112,  115 
Endothermic  reactions,  233,  239 
Enrollment,  i,  9 

Enstatite-wollastonite     equilibrium  di- 
agram, 34 

Equation  of  thermo-couple,  63 
Equilibrium,  19 
Equilibrium  diagram,  70 

ferrite-cementite,  127,  131 

iron-carbon,  126, 131 


Equilibrium,  salt-water,  74 

wollastonite-enstatite,  34 
Equipment,  general  laboratory,  IV,  3 

metallography,  90,  176 
Etching,  80,  177 

agents  for  steel,  167 

antimony,  83 

pits,  169 

polished  specimens,  80 
Eutectic,  34,  73,  127 

appearance,  73 

cementite,  213 

properties,  73 
Eutectoid,  127 
Exfoliation,  189 
Exothermic  reactions,  233 
Expansion  at  Ar3,  143 

Facings,  278 
False  cheek,  288 
Ferrite,  126 

Ferrite-cementite  equilibrium  diagram, 
127,  131 

etching,  168,  173 

habit,  173 

hardness,  173 
Ferroxyl  test,  203 
Fery  radiation  pyrometer,  113 

focusing,  114 

limitations,  114 
Figures  in  written  work,  295 
Files,  heat  treatment,  163 
Filing  notes,  300 
Fire  clay,  melting-point,  25 
Fixing  negatives,  92 

prints,  93 

Flame  temperatures,  257 
Flasks,  274,  281,  288 
Flat-back  pattern,  270,  288 
Floating  cores,  286 
Floor  molding,  280 
Flow-off,  288 
Flue  dust,  analysis,  263 

gases,  composition,  245 
Fogged  negatives,  88 
Forge  fire,  making,  158 
Formulas,  292 


INDEX 


307 


Foundry  equipment,  282 
Fracture,  crystalline,  135 

practice,  269 

examination,  133 

rail,  134 

steels,  138 

tests,  133 

Freezing-point  table,  66 
Fuel,  heat  of  combustion,  247 
Fullers,  heat  treatment,  165 
Furnace,  atmosphere,  10 

burden,  262 

cementation,  187 

charges,  262 

electric,  102-106 

heat  treatment,  142 

oven,  see  Oven-furnace. 

Gaggers,  288 
Gamma  iron,  126 

crystallization,  154 

density,  154 

hardness,  154 
Gangue,  32,  33 

Gases,  volume  and  pressure   relation, 
240 

volume  :  weight  relation,  241 
Gate,  288 

Gay-Lussac,  law  of,  240 
General  apparatus,  2 

laboratory  equipment  IV,  3 
Glasses,  composition,  35 
Glossary,  287 
Goggles,  2 

Goutal's  formula,  250 
Grade  of  steel,  162 
Grades,  method  of  computing,  4,  5 
Grain,  refining,  135,  137 
Granite  points,  heat  treatment,  163 
Granular  pearlite,  172 
Graphs,  see  Curves. 
Graphite  crucibles,  treatment,  60 

in  cast  iron,  215,  217 
Graver  tools,  heat  treatment,  163 
Gray  cast  iron,  215 
Green  cores,  288 
Green  sand,  288 


Green  match,  288 
molds,  280 

Halation,  88 

Hammers,  heat  treatment,  163,  164 

Hardening,  141 

allotropic  theory,  154 

alloy  steels,  153 

carbon,  141 

cracks,  142 

development  of  metarals,  152 

theories,  153,  154 
Hardness,  78,  94 

indentation,  95,  100 

numeral,  96,  100 

rebounding,  94 
Heat  available  in  boiler  fuel,  255 

conduction,  105 

convection,  105 

control,  142 

evolution  of  reactions,  232,  233,  235, 
252 

in  quenching  bath,  147 

mechanical  equivalent,  103 

radiation,  106 

transfer  in  furnaces,  104 

treatment,  see  Annealing  and  quench- 
ing. 

unit,  233 
Heating  curve  of  furnace,  9 

furnace,  19,  142 

power  of  liquids,  147 

practice,  141 
High-speed  steel,  162 
High-temperature  reactions,  252 
History  of  metallography,  167 
Holborn    and    Kurlbaum    pyrometer, 
120 

limitations,  121 

operation,  121 
Hot  bodies,  color  of,  116 

water  systems,  corrosion,  204 

working  of  steel,  135 
Hours  for  work,  i,  4 
Howe's  diagram,  131 
Humphrey's  theory  of  hardening,  154 
Hydrates,  thermochemistry,  235 


308 


INDEX 


Hydrocarbon    cementing   agents,    185, 

187 

thermochemistry,  235 
Hypereutectoid  steel,  173 
Hypoeutectoid  steel,  172 

Illumination  of  opaque  specimens,  79 

Illuminator,  vertical,  79 

Illustrations,  295 

Impact  testing,  139 

Incandescent  bodies,  color,  116 

Indentation  hardness,  95,  100 

Indicators,  203 

Induction  furnace,  104 

Ink,  292 

Inspection  of  rails,  134 

Internal  strains  142,  286 

Inverse-rate  curves,  76,  129 

lonization,  195 

Iron,  allotropy,  126 

carbide,  127 

-carbon  equilibrium  diagram,  126, 131 

cooling  curve,  126 

reduction,  23 

Joint,  288 
Joule,  102 

Keep's  test  bars,  209,  220 
Knives,  heat  treatment,  164 

Laboratory  of  furnace,  7 

tube  furnace,  106 
Ladles,  284 
Latent  heat,  57,  238 
Lathe  tools,  heat  treatment,  163 
Lead-antimony  alloys,  70 

cooling  curves,  58 

melting-point,  66 

reduction,  22 

refining,  13 
Le  Chatelier  optical  pyrometer,  117 

theory  of  hardening,  154 
Lenses  for  metallography,  79 
Lesson  assignments,  3 
Lifters,  291 
Lighting  furnace,  9 


Limestone,  analysis,  263 
Lithium  metasilicate,  melting-point,  66 
Loading  plate  holders,  91 
Loam,  288 
molding,  278 

Machine-made  molds,  281 
Magnesite  brick,  28 
Magnetic  testing,  299 
Mandrels,  heat  treatment,  163 
Manganese  in  cast  iron,  218 
Manuscripts,  296 
Margins,  292 
Martensite,  155,  169 

etching,  169 

hardness,  169 

photo-micrograph,  155,  156 
Mason's  tools,  heat  treatment,  164 
Mass  conversion,  242 
Match  molding,  276,  277 
Matte,  20,  263 
Maximum  temperature,  7 
McCance's  theory  of  hardening,  154 
Mean  specific  heat,  253 
Mechanical  equivalent  of  heat,  103 
Media  for  quenching,  147 
Melting  practice  for  white  metal,  78,  82 

zone,  288 
Metallic  specimens,  care  and  storage, 

i7S 
Metallography,  79 

equipment,  90,  176 

historical  development,  163 

microscope,  79,  83 

steels,  167 

utility,  173 

Metal  protection  tubes,  52 
Metallurgy: 

laboratory  work,  6 

progress,  40 

reagents,  36 

Metals,  constitution,  134 
Metric  mass  conversion,  242 
Microscope,  metallographic,  79-83     ' 
Microscopic  analysis,  93 
Mill  scale,  formation,  13 

rust  inhibitor,  204 


INDEX 


309 


Mine  water,  199 

Modifications,  allotropic,  126 

Moh's  scale,  94 

Mol,  227 

Mold  board,  288 

Molding,  209,  270-290 

equipment,  281 

loam,  278 

machines,  281 

operations,  270 

sand,  278 

skill,  273 

sweeps,  277 

tools,  289 

Molds,  classification,  280 
Molecular  equivalence,  260 

movements,  125 

volume,  241 

weight,  227 
Molecule,  gaseous,  231 

size,  241 

Monochromatic  light,  87 
Morse  pyrometer,  120 

limitations,  121 

operation,  121 
Mother  liquor,  71 
Mottled  cast  iron,  216 
Mounting  of  opaque  specimens,  80,  82 

Naphthalene,  boiling-point,  66 
Natural  gas  analysis,  249 
Negatives,  faults,  88 
Neutral  atmosphere,  10,  18 

refractory,  27 
Nickel,  melting-point,  66 
Nitrides,  thermochemistry,  235 
Noble  metal  couples,  51 
Notes,  filing  of,  300 
Nowel,  288 

Ohm's  law,  41,  102 

Oil  baths,  148 

Open-hearth  furnaces,  26,  28 

heating,  258 
Optical  pyrometers,  78 

calibration,  112 

Holborn  and  Kurlbaum,  120 


Optical  pyrometers,  Le  Chatelier,  117 

Morse,  120 

precautions  in  use,  122 

principle,  116 

Shore,  118 

Wanner,  119 

Orthochromatic  plates,  87 
Osmond's  theory  of  hardening,  154 
Osmotic  pressure,  194 
Outline  of  reports,  297 
Oven  furnace,  care,  2 

construction,  7 

lighting,  9 

operations,  7 
Over-exposure,  87 
Oxidation  of  metals,  13 
Oxides,  thermochemistry,  235 
Oxidizing  atmosphere,  10,  18 

reactions,  6,  12 
Oxygen,  12 
Oxy-hydrogen  flame,  233 

temperature,  257 

Page  numbering,  292 
Palladium,  melting-point,  66 
Paper,  292 

photographic,  87-92 
Paragraph  indentation,  292 
Partial  cementation,  180 
Parting,  288 

Passive  state  of  metals,  199 
Pattern,  270,  278 

pieces,  278 
Pearlite: 

composition,  172 

constitution,  171,  173 

formation,  172 

granular,  172 

spheroidal,  172 

Peen  hammers,  heat  treatment,  163 
Peg  gate,  288 
Peltier  effect,  43 
Personal  apparatus,  2 
Phenolphthalein,  203 
Phosphorus  in  cast  iron,  218 
Photographic  paper,  87 

development,  88 


310 


INDEX 


Photographic  printing,  92 
Photographic  plates,  87 

development,  87,  92 

exposure,  87 
Photomicrography,  86-91 

lighting,  87 
Pickling  vats,  284 
Pig  iron,  fracture,  133 
Pit  molds,  280 
Plane  glass  reflector,  79 
Plates,  photomicrographic,  87 

handling,  91 

loading,  91 

orthochromatic,  87 

Plate  steel,  photomicrograph,  173,  174 
Plating  metal  from  solution,  198 
Platinum  couples,  51 

melting-point,  66 
Polarization,  198,  199 
Polishing  machines,  1 73-1 75 

metal  specimens,  80,  82,  173 
Potential  drop,  102 
Pot  furnace,  107,  108 
Pouring  basin,  289 

iron,  299 

Pressure  of  atmosphere,  240 
Primary  battery,  42 

cells,  197,  205 

ferrite,  172 
Prints,  photographic,  88 

faults,  88 

manipulation,  92 

Problems,  method  of  solution,  227 
Process  plates,  87 
Producer  gas,  analysis,  243 
Protection  tubes,  52 
Proximate  analysis,  249 

heat  calculation,  250 
Pumping,  289 

Punches,  heat  treatment,  164 
Pyrometers: 

calibration,  63,  112 

optical,  in 

radiation,  in 

Seger  cones,  8 

thermoelectric,  41 
Pyroscope,  Shore,  118 


Quartz,  allotropy,  25 

melting-point,  25 

protection  tube,  52 
Quenching,  143-148 

baths,  148 

fluids,  148 

mechanism  of,  147 

media,  147 

power  of  fluids,  147 
Queries,  assignment,  4 

grades,  4 

Rabble,  15 
Radiation,  106,  115 

laws,  106,  in,  115 

pyrometers,  in 

calibration,  112 

Fery,  113 

limitations,  112,  114 

selective,  114 
Rails,  fracture,  134 

inspection,  134 

molds,  273 
Rapping  bar,  290 
Ramming  bars,  290 
Rare  metal  recovery,  13 
Rattling  barrels,  284 
Ray  filter,  87 

Razors,  heat  treatment,  163 
Reactions,  233,  239 
Reamers,  heat  treatment,  164 
Rebounding  hardness,  94 
Red  radiations,  115 
Reducing  atmosphere,  10,  18 

reactions,  6,  18 
Refining  grain  of  metals,  135,  137 

lead,  13 
Reflector,  79 

Regenerative  principle,  256, 
Refractories,  6,  25 

acid,  27 

basic,  27 

binder,  ,27 

cement,  54 

classification,  27 

manufacture,  26 

melting-point,  25 


INDEX 


311 


Relief  polishing,  80 
Replacement  of  metal  in  solution,  198 
Resistance  furnaces,  104 
Resistivity,  41,  105,  106 
Reverberatory,  charge,  263 

operation,  264,  266 
Riddle,  289 
Rigging,  282 
Riser,  289 

Roasting,  13,  15,  266 
Roll  call,  i 
Runner,  289 

Safety  precautions: 

goggles,  i 

lead  fumes,  16 

lighting  furnaces,  9 

pouring  metals,  22 
Salt  baths,  142,  148 

solutions,  71 

volatility,  68 

-water  system,  70 
Sand  holes,  285 

molding,  278 
Scabs,  285,  289 
Scale,  formation,  13 

pivots,  heat  treatment,  163 
Scleroscope,  94,  98 

limitations,  97 

use,  98 

Scratch  hardness,  94 
Seger  cones,  8 

composition,  36 

manufacture,  30 
Selective  radiation,  114,  115 
Sensible  heat,  56,  254 
Sets,  heat  treatment,  165 
Shape  factor,  105,  106 
Sheaves,  molding,  274 
Shore  pyroscope,  118 

scleroscope,  94-98 
limitations,  97 
use,  98 
Shot,  289 
Shrinkage,  286 
Shrink  head,  289 

holes,  285 


Siemen's  regenerative  principle,  256 
Sighting  tube,  114 
Silica,  allotropy,  25 

brick,  28 

melting-point,  25 

protection  tube,  52 
Silicates,  thermochemistry,  236 
Silicate  slags,  33 
Silicon  in  cast  iron,  217 
Silver,  melting-point,  66 
Sketches,  295 
Skim  gate,  289 
Skin-dried  molds,  280,  289 
Slags,  32 

Sledges,  heat  treatment,  164 
Slickers,  290 
Slicking  of  molds,  273 
Slotters,  heat  treatment,  163 
Snap  flask,  289 

Sodium  chloride,  melting-point,  66 
Soldering,  46 
Soldier,  289 
Solid  solution,  35,  127 
Solution,  194 

pressure,  194 

salt,  71 

Solution  of  problems,  227 
Sorbite,  155,  171 

etching,  171 

hardness,  171 

photomicrograph,  156 
Special  apparatus,  3 
Specific  gravity  of  gases,  241 
Specific  heat,  252,  253 
Specimens,  illuminating,  79 

mounting,  80,  82 
Spheroidal  pearlite,  172 
Split  patterns,  274 
Sponginess  in  castings,  285 
Spotty  prints,  88 
Spring  draw  nail,  290 
Sprue,  289,  290 
Squad  organization,  i,  9 
Stains  on  negatives,  88 
Standard  pressure  and  temperature, 

240 
'    Standardization,  see  Calibration 


312 


INDEX 


Stead's  brittleness,  135 
Steel,  blister,  181 

boilerplate,  173,  1 74 

burned,  135 

cooling  curves,  126,  129 

crucible,  162 

crystallization,  133 

equilibrium  diagram,  1 26,  131 

experiments,  124 

fracture,  133 

hardening,  141 

metallography,  167 

photomicrographs,  135 
Stefan's  law,  106,  in 
Strains  in  castings,  286 
Strike,  290 

Sulfates,  thermochemistry,  236 
Sulfide,  ores,  13 

roasting,  13 

test,  15 

thermochemistry,  236 
Sulfur,  allotropy,  126 

boiling-point,  66 

boiling-point  apparatus,  46 

in  cast  iron,  217 
Supplies,  3 

Surface  resistance,  105,  106 
Swab,  290 

Swages,  heat  treatment,  164 
Sweep,  277,  289 

finger,  278 

Temper,  162,  163 
Temperature  control,  40 

minimum  for  carburization,  180 
Tempering  steel,  155,  157,  162 

baths,  157 

colors',  157 

Test  bars,  casting,  209,  220 
Texts,  3 
Thermal  analysis,  125 

units,  233 
Thermochemistry,  232  e.s. 

at  high  temperature,  252 

data,  235 
Thermo-couple  calibration,  63 

constitution,  49 


Thermo-couple  cost,  50 

elements,  41,  49 

melting-point,  50 

sizes,  50 

stability,  50 

Thermo-electric  equation,  63 
Tight  flasks,  289 
Time,  a  factor  in  transformation,  152 

of  exposure,  87 
Tin,  melting-point,  66 
Tool  making,  162 

steel,  162 

Total  cementation,  180 
Toughening,  157 

Track-layers'  tools,  heat  treatment,  164 
Transite  board,  working  of,  109 
Troostite,  171 

etching,  171 

hardness,  171 

photomicrograph,  156 
Transformation  point,  125 

apparatus,  128 

suppression,  152 

time  factor,  152 
Tridymite,  25 
Tube  furnace,  106-108 
Tubes,  protection,  52 
Tumbling  barrels,  284 
Tuyeres,  283,  289 

Ultimate  strength  derived  from  hard- 
ness, 96 

Underexposure,  87 
Upset,  289 

Vats,  pickling,  284 
Vent,  289 

wires,  290 

Vertical  illuminator,  79 
Volume  relation  in  equations,  231 

Wanner  pyrometer,  119 

calibration,  120 

limitations,  120 
Warping  in  castings,  286 

in  heat  treatment,  142 
Water,  cooling  curve,  58 


INDEX 


313 


Water,  latent  heat,  238 

-salt  equilibrium  system,  70 
specific  gravity,  241 

Wedges,  heat  treatment,  165 

Wedging-up  molding,  275 

Weight  relation  in  equations,  225 

Welder,  45 

Whirl  gate,  289 

White  cast  iron,  215 

White  metal,  melting,  75,  82 


Witherite,  cementing  agent,  183 
Wollastonite  :  enstatite  equilibrium  dia- 
gram, 34 

Work  of  electrical  current,  102 
Working  steel,  135 
Written  work,  4,  5,  292 
Wrought  iron,  corrosion,  203 

Zinc  burning,  13,  15 
Zinc,  melting-point,  66 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 
BERKELEY 

Return  to  desk  from  which  borrowed. 
This  book  is  DUE  on  the  last  date  stamped  below. 


MINERAL  TECHNOLOGY  LIBRARY 


1  3  19 


LD  21-100m-9,'48(B399sl6)476 


376245 


UNIVERSITY  OF  CALIFORNIA  LIBRARY 


